If you mean series 6, the 6th season of the new series in 2011: At the end of "The Wedding of River Song", the 11th Doctor is 1103 years old, if you believe what he says about his age. There are many reasons not to believe him on this subject, as outlined in the answer to the question How old is the Doctor? We don't know how much time had passed in the Doctor's timeline between "The Wedding of River Song" and the Doctor, the Widow and the Wardrobe, but it may only be a short time.
If you mean season 6, the 6th season of the classic series in 1969: At the end of "The War Games", we don't know the 2nd Doctor's age. He said he was about 450 in 1967's Tomb of the Cybermen. The 3rd Doctor implied he was several thousand years old in 1970's "Doctor Who and the Silurians" and directly said he was several thousand somethings (he didn't finish the word) in 1971's "The Mind of Evil".