In the Doctor Who universe, pretty much anything is possible. Spiders can talk, the Titanic can fly, the wi-fi can eat you, and - perhaps most impressively of all - people can live to be billions of years old, without needing a single drop of anti-wrinkle cream.
In a world of regenerating Time Lords, indestructible immortals, and ageless robots, it's no surprise that people can hit some truly incredible ages, but out of all the characters in the Whoniverse... who lived to be the oldest?
Since this is a show about time travel, that's a difficult - but not impossible - question to answer. Some characters state their ages out loud, while others can be worked out thanks to the sheer depth and detail of Doctor Who lore. So let's do it!
Before we get going, here's a quick ground rule: any characters that are only mentioned in passing - i.e. "I once knew a thousand-year-old sentient golf ball from the planet Vworp" - are disqualified, on the basis that these are meaningless jokes, not proper characters. Also, sentient golf balls are terrifying.
10. Madame Vastra (And Other Silurians)
Estimated Age: Hundreds of years.
The Silurians were the original masters of Earth, ruling over the planet long before we humans rose to dominance. Most of their appearances in the show revolve around them trying to reclaim the Earth for themselves, because they feel like they have more of a right to it than we do. Fair point, considering that they were here first!
Since the Silurians pre-date humanity, we know that the entire species is millions and millions of years old. In Series 5's The Hungry Earth - which takes place in the modern day - the Eleventh Doctor tells a Silurian soldier that she is "three hundred million years" out of her comfort zone.
However, since this soldier has been hibernating for most of that time, this isn't the actual lifespan of a Silurian - the hibernation process puts them into suspended animation, halting ageing. A Silurian's proper lifespan is a lot less lengthy, clocking in at several hundred years. Still, it's an impressive age, and outside their hibernation units, Silurians like Madame Vastra - who would be hundreds of years old in the 21st century - will be around for quite some time.
The Sea Devils (basically aquatic Silurians) also likely have similar lifespans.