In my view, the simple answer to the OP original question is - as a 74 year old, I will go on flying as long as I can and as long as I want to.
Like most pilots I know I am intensely self critical about my flying and I know that, when I don't do well in my own eyes, I do not enjoy it. Too many of those flights and I will stop. In the last couple of Winters I am aware that there are more days when I cannot be bothered to get the aircraft out because I feel the cold more than I did.
I frequently ask fellow pilots this question and, so far, everyone encourages me to go on as if it is ridiculous for me even to think about giving up. Some of them I fly with fairly often and they seem happy to fly with me.
I once thought that I would give up when I found myself making mistakes but then I realised that I have always made mistakes. Perhaps, if those mistakes become more serious, like flying with one mag switched off, I will give up.
Having operated with a NPPL for the last few years, my doctor has said that he wants to see me before he will sign another Declaration so it may be, in a couple of months, that he will put a stop to my flying.
Having given up flying for 23 years because of cost and family commitments, I am reluctant to stop again with out good reason.