Triska
The fact that BBC have a way of not going with continuity. The Doctor was 941 years old back when he was beginning his seventh life. So, don't read too much into it.
I don't know about you but if I was getting up to the high hundreds in years, I'd start lying about my age. Seriously, it must be a bit difficult keeping track of the years, and are those even Earth years? Are they relative to the time he is in when he quotes his age?