How old was each actor when they became the Doctor?

Age is an incredibly difficult concept to pin down when it comes to Doctor Who because the show is unreliable with it. The Third Doctor mentioned being thousands of years old on multiple occasions, yet the Tenth Doctor was happily in his 900s. This may be caused by different measures of time—as the Second Doctor specified that his age was determined by "count[ing] in Earth terms"—a tricky memory, or just inconsistencies in the writing.

On top of that, the time travel nature of the show makes it virtually impossible to use appearance as an indication of age. After all, Alex Kingston was at her youngest when her character was at her oldest, which prompted the lamp-shading comment that she "might take the age down a little, just gradually, to freak people out."

This can make it interesting to explore the actors' ages, particularly when fans try to argue that an actor like Matt Smith was too young for the role, or Peter Capaldi was too old. The Doctor has been played by actors as young as 27 or as old as 80, and so long as they play the part well, it doesn't have much, if any, impact on the show.

Here, we break down all fourteen main actors to play the titular role, as well as three actors who took on the mantle in more complicated ways. How old were they when they started and finished their runs, and how did that line up with the character's age? All that and more is discussed below.

Jo Martin

Birthday: April 29, 1980

Jo Martin played the Fugitive Doctor, a version of the character heavily implied to predate any version previously depicted on the show. She appeared in four episodes of the series, from 2020 to 2022, and played a major role in explaining the Division and the Timeless Child arc. Martin was 39 when her first episode debuted, and 42 years old when last shown.

William Hartnell

Birthday: January 8, 1908

William Hartnell is responsible for the first official version of the Doctor, playing the lead from the show's debut in 1963 until his exit in 1966. Although the Doctor's age is incredibly difficult to account for, this version was presumed to have lived for several centuries, having been 236 when he stole the TARDIS. The character has been stated to have been either 450 or 900 when he regenerated in 1966.

The actor's age is much easier to track, having been 55 when the show began and 58 when he left. However, he did return for "The Three Doctors" in 1972, where (despite playing a younger version of the character) he was 64 years old. Sadly, he passed away on April 23, 1975, which led to other actors taking on the role for future appearances.

David Bradley

Birthday: April 17, 1942

Despite Hartnell's death, the First Doctor had multiple additional appearances. He was played by Richard Hurndall (age 73) in "The Five Doctors" special and has been portrayed by David Bradley in three appearances from 2017 to 2022. At that time, his age ranged from 75 to 80 years old. In both cases, the replacement actors were decades older than Hartnell, which might contribute to the popular misunderstanding that Hartnell was the oldest leading actor.

Patrick Troughton

Birthday: March 25, 1920

Patrick Troughton was the first actor to take over the role of the Doctor from another actor, having to pull off the concept of regeneration for the first time. Generally, it is believed that the Doctor was between four and five hundred years old when he regenerated the first time, but it's unclear how many years he spent in his second form.

Patrick Troughton was 46 when his first episode premiered, about ten years younger than his predecessor. He stayed in the role for just under three years, but then returned in "The Three Doctors" at age 52, "The Five Doctors" at age 63, and "The Two Doctors" at age 64.

Jon Pertwee

Birthday: July 7, 1919

Jon Pertwee joined Doctor Who in 1970 as the Third Doctor, who spent most of his run on Earth, working alongside UNIT. Fans don't get much, if any, reliable information about how old he was during this time period, as he consistently referred to himself as being thousands of years old. This doesn't fit the timeline established by later Doctors, so the best information actually comes from the next version of the character, who claimed to be 748 after regenerating.

Pertwee is easier to pin down, as he was 50 when his first episode aired and 54 when he regenerated. However, he also returned in "The Five Doctors" at age 64, which adds a bit of "timey-wimey" energy to his portrayal, since his character during the special would have been from some point during the original run.

Tom Baker

Birthday: January 20, 1934

Tom Baker's version of the Doctor is probably the most widely-known version from Classic Who, in large part because he was the lead for seven years. During that time, he almost always referred to himself as being 750 years old, although some adventures were noted to last decades on their own. This is the point where the Doctor really seems to lose track of his age, though it's likely that he was in this form for around 50 years.

Although Tom Baker did not spend that long as the Doctor in the show, he has been very active in audio dramas in the decades since. When his first episodes aired, Baker was 40 years old, the youngest actor to take on the lead at that point. He was 47 when he officially left the show, but he continued to voice the role for years and returned as The Curator in the 50th anniversary special "The Day of the Doctor" at age 79.

Peter Davison

Birthday: April 13, 1951

Peter Davison had the unenviable task of taking over from Tom Baker and making the fandom accept a new version of the Doctor. The Fifth Doctor never discussed his age during the television series, but audio and written stories mark his version of the character as being approximately 800-900 years old.

Davison himself was much younger, taking the title of youngest actor from Tom Baker. When he first appeared on the show, Peter Davison was 29, and he left at age 32. He would remain the youngest actor to take on the role until Matt Smith came in 2010. Thanks to being so young when he joined the franchise, Davison is one of the four Classic Era actors who returned for "The Power of the Doctor," during which he was 71 years old.

Colin Baker

Birthday: June 8, 1943

Colin Baker was actually in the "Arc of Infinity" serial during Peter Davison's run, but it wasn't until 1984 that he joined Doctor Who as the Doctor. Perhaps because of how unclear it was in earlier runs, the show directly stated the Doctor's age on multiple occasions during this era. He was around 900 at the start of Baker's tenure and was 953 when he regenerated.

Although over 50 years had passed in the show, Baker only held the role for two and a half in the real world. He was 40 when he first appeared as the Doctor, ending his time on the show at age 43. Like Davison, Colin Baker returned to the role in "The Power of the Doctor," when he was 79 years old.

Sylvester McCoy

Birthday: August 20, 1943

Sylvester McCoy was the last actor to play the Doctor during the show's original run, as it ended on December 6, 1989. In that time, he did not regenerate, so it's unclear precisely how long he would have kept that form. Several novels mention him passing 1,000 years old, but that was retconned in the revival when the character was defined as still being in his 900s.

When McCoy's first episode premiered, he was 44 years old. When the show ended, he was 46. However, he was still officially the Doctor afterward, returning for the television movie in 1996. When his version of the Doctor regenerated in the movie, McCoy was 52. Although that was the end of his official tenure as the character, he would also return for "The Power of the Doctor" at age 79.

Paul McGann

Birthday: November 14, 1959

Paul McGann played the Eighth Doctor, who only appeared in the television movie. Despite having so little screen time, the Eighth Doctor was the longest-lasting version of the character, as he was used in non-televised content from 1996 until 2005. In written and audio adventures, he frequently claimed to be over 1,000 years old, and one adventure theoretically lasted 600 years, making his in-universe tenure longer than any other form after Hartnell's.

When the TV movie debuted, McGann was just 36 years old, with the potential to play the part for a long time if it was picked up. However, there were no future movies or television episodes, and the 2005 revival started with Christopher Eccleston in the lead. However, McGann has since returned to the screen twice, regenerating into the War Doctor in the minisode "The Night of the Doctor" at age 54 and appearing as one of the Guardians of the Edge in "The Power of the Doctor" at 63.

John Hurt

Birthday: January 22, 1940

John Hurt, like Jo Martin, falls earlier in the Doctor's timeline than in the show's release schedule. He plays the War Doctor, a version of the character that was erased from his understanding of himself due to the actions he took during the Time War. The War Doctor was created for the show's 50th anniversary, and thus audiences don't know much about him beyond what happened in that special.

Technically, John Hurt's first appearance was on May 18, 2013, in "The Name of the Doctor," which came out when Hurt was 73. His other two appearances debuted later that year, with most of his screentime coming in "The Day of the Doctor," alongside David Tennant and Matt Smith. Hurt did work on several audio dramas for the character but passed away in 2017 without any further televised appearances.

Christopher Eccleston

Birthday: February 16, 1964

Christopher Eccleston's Ninth Doctor was the first in the revival, which gave him a permanent place in the minds of many fans. When he was first introduced, he was the last of his species, the rest of whom had been destroyed in the Time War. He mentioned that he'd spent 900 years traveling, which technically would make him around 1100, since other sources put him in his 200s when he left Gallifrey.

Eccleston, meanwhile, was 41 when the first series aired. This was fairly normal for actors in the role, though it was somewhat old given his romantic undertones with the 18-year-old Rose Tyler (and 22-year-old Billie Piper). He only stayed for one season and has not returned to screens, making him one of the few actors to never return after his original tenure.

David Tennant

Birthday: April 18, 1971

David Tennant is undoubtedly the most complicated actor when it comes to time on Doctor Who, and age is no exception. As the modern actor who has been in the most episodes, it's no surprise that he has taken on the role at many different ages.

Originally, Tennant joined the show as the Tenth Doctor during the second, third, and fourth seasons. During that time, the character was said to be around 900, regenerating when he was 906. This became the new benchmark for the character's age, despite its contradictions with earlier claims. Notably, this would have been the shortest lifespan for the character thus far, as all the others had lived at least decades (if not centuries) between regenerations.

However, Jodie Whittaker's version of the Doctor regenerated back to David Tennant in 2022, so he also played the Fourteenth Doctor. This version of the character bi-generated into Ncuti Gatwa's version, which allowed him to continue living in Tennant's form (and get therapy) while Gatwa's Fifteenth Doctor was responsible for living the life of the Doctor.

David Tennant was 34 when his first episode aired and 38 when the Tenth Doctor regenerated in "The End of Time." However, he also appeared in "The Day of the Doctor," which is set in his personal timeline after season 4 but before his regeneration. When the special debuted, Tennant was 42.

While they might have been able to disguise his aging at that point, he was obviously much older when he returned as the Fourteenth Doctor at age 51. The bi-generation episode aired when he was 52, but his character's survival means he could show up as that version of the character at any point in the future. Alternatively, the human version of the Tenth Doctor is still around in an alternate universe, so he could reappear in that form as well.

Matt Smith

Birthday: October 28, 1982

Since David Tennant was the most popular version of the Doctor since Tom Baker, Matt Smith had his work cut out for him as the Eleventh Doctor. However, he was able to win over fans with his ability to alternate between acting as young as his physical form and as old as the character. Though the Doctor was 906 when he first took Matt Smith's form, he was said to have lived around 300 years during his three seasons, as well as another 900 at Trenzalore. By the time he regenerated, the Eleventh Doctor would have been over 2000.

This was an impressive thing to pull off for an actor who was so young. Matt Smith was 27 when he first appeared as the Doctor and only 31 when he left. He is the youngest person ever cast as the Doctor, which means he will have plenty of opportunities to reprise the role if he chooses to.

Peter Capaldi

Birthday: April 14, 1958

Given how long the Doctor lived during Matt Smith's era, it's no wonder he wanted a more mature appearance the next time around. Through most of his run, the Twelfth Doctor was identified as being around 2,000 years old, though he had several arcs that took place over decades or centuries. In "Hell Bent," the Doctor theoretically lived around 4.5 billion years, although that is rarely counted in his age.

Given how much time passed during the Eleventh and Twelfth Doctors' timelines, it makes sense that Peter Capaldi was older than his recent predecessors. His first episode as the Doctor came out when he was 55, the same age as William Hartnell when he debuted. He stayed in the role until he was 59, which made him the oldest actor to play an "official" version of the Doctor during their original run.

Jodie Whittaker

Birthday: June 17, 1982

Jodie Whittaker played the Thirteenth Doctor, who was relatively distant from her companions, given the traumas her previous versions had gone through. She claimed to not know how old she was anymore, although the number was stated to be in the thousands. In the game Lost in Time, she had a 5,000-year diary, which would seem to indicate that a few more millennia had passed.

While the character may have forgotten her age, the actor was easier to track. Whittaker was 35 when she first appeared on Doctor Who, eventually leaving the show at age 40. Interestingly, she was born in the same year as Matt Smith, making it likely that she will have as many future comeback opportunities as he will.

Ncuti Gatwa

Birthday: October 15, 1992

The current iteration of the Doctor is known as the Fifteenth Doctor, although the Timeless Child arc makes it impossible to say how many previous forms the Doctor may have had. Accepting that fact, the Fifteenth Doctor hasn't bothered trying to quantify his age. This is likely going to be the case moving forward, as the Doctor's experiences on and off screen are virtually incalculable.

Actor Ncuti Gatwa is an interesting choice for this, as his previous prominent role was as teenage Eric Effiong on Sex Education. When he first debuted on Doctor Who, Gatwa was 31 years old, putting him on the younger end of the scale. Only time will tell how long he stays in the role, but he has thus far managed to play the character as functionally without an age, which has intriguing potential for the future.