In 1925 The Doctor mentions to Donna he’s a billion years old. I refuse to believe this is the truth due to what we’ve seen of the other Doctor’s ages, I believe the Doctor was speaking in hyperbole given the context it was used, to highlight he can’t talk about everyone he ever meets.

I know there’s been massive inconsistencies in the doctor’s age across the series, but the revived era has treated the 900 as being his true age.

The Tenth Doctor is 906 when he regenerates

The Eleventh Doctor, last states he’s 1103, plus 900 years on Trenzalore, taking us to 2003 at Minimum, there’s a bit of play depending how long he spent between series 6 and 7 on his own.

The Twelfth Doctor claims he’s “over 2000 years old” which is true. He then spends 24 years on Trenzalore, and 70 years guarding the vault, making Twelve, at the time of his regeneration, around 2097.

The Thirteenth Doctor spent 19 years in space jail pushing us to 2116, and given The Eleventh Doctor began to present as “old” after about 500 years (200 years he spent travelling 300 years on Trenzalore), and Thirteen doesn’t look much older at the end of her life than at the start.

One could argue the confession dial, but he said “a billion” not 4.5 billion.

Essentially what I’m saying is the Doctor can’t be a billion years old at this point, as it would have occurred in Jodie’s run.

Personally I don’t think it works for the character, being a billion years old reduces the emotional weight of the doctor’s adventures we actually see on screen, and wouldn’t fit with how we know the Doctor’s faces age