.. Question is, will each person know when it is time.

My father was a long-time pilot, and when he hit 60, he told me he started to carry a $100 bill in his wallet. It was for the first guy who told him it was time to hang it up and stop flying. Since he made the decision to quit on his own, he gave the $100 to the kids on the flight line who used to help him pull his Bonanza out of the hangar, fuel it and wash it. If I remember correctly, he gave several of these $100 bills out to more than just a few line kids.