Back in September, I posted on this blog about the Doctor's age. That held fairly accurate until yesterday. The Time of the Doctor has added to that. First a brief rundown.
236 - when he borrowed the Tardis (or it borrowed him)
450 - or there abouts at the time of his first regeneration
600 - or there abouts at the time of his second regeneration
750 - give or take a bit at the time of his third regeneration
800 - at the time of his fourth regeneration
900 - at the time of his fifth regeneration
953 - at the time of his sixth regeneration
1136 - when he met Rose and subsequent regenration
1143 - at his most recent regeneration (you might argue it should be 907, but between when he met Rose and he regenerated, his age changed from just traveling in the Tardis for 900 years to being 900 years old, so you have to add in the 236 years before he borrowed the Tardis)
1339 - the most recent age the doctor gave (1103 plus 236)
Yet when he met Clara he reduced to just 1000, rather than 1103, proving that he lies about his age. In The Day of the Doctor he gave his age as roughly 1200 and admitted he wasn't sure because he lies about it so often.
Then we come to Christmas and The Time of the Doctor. We start out with the Doctor over 1300 and then he spends 300 years on Trenzalore in the town of Christmas while Clara clings to the side of the Tardis. Then he sends her away again and spend an unknown time, but enough to age considerably more so I am assuming it is over 300 more years. My best guess is another 500 years. That makes The Time of the Doctor the longest episode in terms of the Doctor's life. He ages 800 years. Starting at 1339 at a minimum, that puts him at 2139 years. It could be considerably more than that and whatever the Doctor says about his age is probably wrong and less than his real age.
So as Peter Capaldi takes the reins to start off the Doctors give of a complete new life cycle (so does this mean 13 more incarnations of the Doctor or 12? Was this regeneration the first of the next 12? Guess we'll seen in another 50 years), he is over 2000 years old, but he probably won't admit that. It will be interesting to see. Not every Doctor states his age, but all of the new ones have.