The mystery of the Doctor’s true age has often been a major point of discussion for Doctor Who fans, who have struggled to make sense of the various conflicting ages the Time Lord has claimed to be over the decades. Obviously, thanks to season 12’s Timeless Child revelations, we now know that the Doctor is in fact much, much older, perhaps millions of years older, than they ever previously realized. But the Doctor never knew about this before, so the debate still stands.
One of the earliest times the Doctor stated their age came in 1967’s “Tomb of the Cybermen” in which the Second Doctor said he was 450 years old. The Third Doctor then said he’d been alive for thousands of years on two separate occasions. The Fourth Doctor later told Sarah Jane that he was around 750, which he joked was middle-aged for his kind. The Sixth and Seventh Doctors, meanwhile, revealed they were about 950. In the modern series, though, the Ninth Doctor declared he was 900.
The most straightforward explanation for the discrepancy is that the Doctor is simply making it up. In “The Day of the Doctor,” the Eleventh Doctor admits to himself – er, his other selves – that he’s “twelve hundred and something, I think, unless I’m lying. I can’t remember.” This is pretty telling, but maybe there’s an alternate explanation, as put forward by ScreenRant. And the root of that lies in what the Second Doctor said way back when.
Doctor No. 2 told companions Jamie and Victoria he was 450 “in Earth terms.” This may tell us that the Doctor only sometimes counts his age in Earth years. We don’t know how long a year is on Gallifrey so some of the estimates of his age could have been gauged by the solar cycle of his homeworld. This could definitely apply to those Third Doctor instances. Gallifreyan years may be much shorter than those on Earth. Therefore, he was thousands of Gallifreyan years old, but in Earth terms, only a few hundred at the time.
Things like the Doctor’s true age will likely never be answered definitely on the show – after all, it is called Doctor Who – but they’re fun to speculate about nonetheless.