I'm just a "kid" at 62, but my last trip was when I was 59. Recent misses due to economic/job related circumstances, not physical or mental problems, although some might disagree on the mental part ;D

We have people here well into their 70's I believe.
I've talked to a couple in the Q who were well into their 80's.

Old age isn't what it used to be. If you keep fit, and still have your mental faculties, then with some planning and a little common sense, you can trip solo until you can't physically handle it or read your maps/GPS ;)

I plan on soling until either or both of the above conditions occur.
It might just be a short base camp trip with little if any portages, but I'll be doing something.

I'd rather drop dead doing what I love, than die tied to the couch/rocking chair or hospital bed, stuck full of tubes and hoses ;)