My dad was 87 the last time I took him to the range. He decided it was his last time due to his congestive heart failure and resulting problems of physical stamina, and because he feared lack of concentration would cause a safety issue. (He has minor memory issues, but he was mainly referring to the fact that his breathing is so bad that it distracts him.) He had made the same decision about working in his work shop a little earlier, and I respected his decision with appreciation for the fact that he was cognizant of his own limitations.
He is still here, but doing poorly and hardly gets out of the house. My main point, although I took a circuitous route to it, is that he quit shooting because he had a specific limitation, not because of a number on a calendar.