I think he is ageless..I've always been of that opinion (well, since 3.20), although I
do accept the possibility of him time-travelling - that is also very possible.
I think Ben's sarky remark: "You DO remember birthdays, don't you Richard?" does indicate that he's ageless though..or something to do with the island preserving is age..that kind of thing.
Just my opinion.
I shall move this into T&S, as it's not directly connected to this episode and seems to be a theory.
Please feel free to continue in there tho 