First Doctor - Never stated his age on screen.
Second Doctor - Told Victoria he was ‘Something like 450’
Third Doctor - Claimed to have been a scientist for ‘several thousand’ years
Fourth Doctor - At least 760 by the time he regenerated
Fifth Doctor - Never stated his age on screen
Sixth Doctor - Told Peri he was ‘More or less’ 900-years-old
Seventh Doctor - Claimed to be 953, same age as the Rani
Eight Doctor - Never stated his age on screen.
Ninth Doctor - Told Rose he was 900
Tenth Doctor - 906 when he regenerated
Eleventh Doctor - 1103 by the time he was ‘killed’ at Lake Silencio.
I truly believe he has no idea how old he is, certainly in Earth years, and Gallifreyan years obviously no longer exist so he just makes up a number.