There's a bunch of really badass people doing interesting things and discovering new things well into their 70s. The grandfather of a friend of mine picked up orientation running in his 80s - he's now the national champion of his age group.
I think more than age, what one has to overcome is the reluctancy to try new things. I think being reluctant to do so is natural to humans at any age; the difference is that when we're young we're forced to do so. The more experienced we get the easier it is to fall into all habits, and he who's not busy being born is busy dying, as Dylan said.