People age at very different rates, just as they differ a lot in other things. Ann Welch, who'd been flying all her life, gave up flying in her mid-70s as she didn't feel safe any more. A chap in his 70s at my flying club recently did the same. Some people can go on into their 80s and 90s, some can't.
I hope by the time I get to that kind of age I know myself well enough to know if and when I should give up flying, or give up trying new things in aviation - and to listen and heed the signs! I think that's the key.
Age has got something to do with it, but you can't generalise.