Time Lords are extremely long-lived, routinely counting their ages in terms of centuries; the Second Doctor claimed in "The War Games" that Time Lords could live "practically forever, barring accidents." The series has suggested that Time Lords have a different concept of ageing from humans. In "Pyramids of Mars", the Fourth Doctor considers an age of 750 years to be "middle-aged". In "The Stolen Earth", the Tenth Doctor refers to when his original incarnation was a "kid" at 90 years old. However, within a specific incarnation, a Time Lord is able to age, albeit much more slowly than a human. The War Doctor and Eleventh Doctor, over the course of the Last Great Time War and the Battle of Trenzalore, respectively, are seen to age within their respective incarnations to what would appear to a human to be old age; both conflicts are suggested within the series to last hundreds if not thousands of Earth years.