Lots of interesting comments, many anecdotes on flyers in their 70s, 80s, and 90s, a few posters who seem to be in terror at the mere idea of old age, and even an accusation of ageism for discussing this issue. But.....
I'm not sure anyone has answered Mary's core question, which seems to me to be
how do you decide when the time comes to step down gracefully from flying due to AGE and the inevitable decline in sharpness that comes with old age? Or do you just wait until the medics give you the chop?
The precise age we're talking about is irrelevant. Maybe in your own case you can go on till you're about 120 years old. Or maybe you can't. But how do you know? Would you know? And we're talking about single pilot operations such as private flying, with no-one else around to notice or help. Would the medics even recognise a marginal decrease in the ability to cope with, for instance, an emergency such as a failure of something crucial in bad weather? (apologies to Radgirl for even suggesting this

)
I'm only asking....