I just found another interesting clue, from the bbc web site for doctor who.
The curator in the day of the doctor is played by Tom baker, an early doctor.
Is that going to get worked into a story line, or just a coincident.
That poses an interesting question actually, in the fiftieth anniversary special the Doctor (Matt Smith) says he might settle down and leave it all behind (Doctery stuff I presume) and become a curator, he could do that he says, even curator of this collection... and Tom Baker pops up and says maybe you did, inferring that as the Doctor which he (Tom Baker) is, he did settle down and become curator of that collection.
So the question is actually this, his (Tom Baker's) time as the Doctor ended when he regenerated, and he regenerated when he was younger, so how did he reach old age, put simply, he couldn't.
The implications are that either, after his very last regeneration at some point in the future, he returned to earth, somehow became that particular version of the Doctor again and became curator in order to be there for himself to have that conversation with after he had achieved that ripe old age. Or he (Matt Smith) has run into an alternate version of himself as that previous incarnation of the Doctor (Tom Baker), from a parallel dimension or the like. Or that Doctor (Tom Baker) is not actually the Doctor in that form but as he appears there has some knowledge of that particular doctor and therefore is a clone or a shapeshifter or some such.
If you are not confused yet, the newer Doctor, in this case Matt Smith, can indeed meet up with any older Doctor but only in the way they have already been presented because after they regenerate each doctor as they are before regeneration ceases to be and becomes another version of the Doctor himself, so while the Doctor is a time traveller and can always run into himself or call upon other versions of himself they will always be the age they were when they regenerated, never older. The same way as he (the Doctor) cannot visit a younger version of any Doctor other than the very first Doctor (William Hartnell) before his regeneration, because he is the only one that has had a childhood whereas subsequent Doctors sprang forth at their current age from a regeneration... Phew!
So, unless there is some sort of time distortion or trick by the Master or wizardry of some sort or other fantastical discrepancy, which as you say will perhaps be a later storyline, then there is no way known the Doctor can be older unless he regenerates to an older age as he will with the Peter Capaldi Doctor.
