I've flown with plenty of people well into their sixties who are in far better physical and mental shape than some half their age
True, maybe. I would however expect this to be the minority. Just like you see 67 year olds running a marathon, i.e. they are in the minority.
Wouldn't it be better to just bale out gracefully rather than watch things go downhill and end up being pushed? Lets face it, we can't go on forever. Its quite similar to OAP drivers who continue to drive when you really would rather not have to put up with them, but they just don't know when to call it a day.
When you get to 65 go play golf or do some weeding. There's more to life. By then you'll probably have such a massive airline pilot pension pot that you shouldn't need to do it anymore.