Okay, doesn't a 45 year-old have more chance of dying than a 35 year-old? And so on...
By that logic we should all be safest with fuzzy-cheeked 18 year-olds doing the piloting! Or perhaps computers rather than humans.
Personally, I'd like to see some sort of stress test developed that could show, one way or the other, who's still relatively fit, physically and mentally, and who's past it. You do have some guys who stay fit and others who are crocks in their thirties; just picking an age isn't the full answer.
Years ago there was a story, true I believe, about a pilot dropping dead at the door as he was on his way out of the Medical Centre at Gatwick with a fresh Class I in his pocket.