I saw a study put together about 6 years ago on this issue, and it was quite fascinating. They ranked it in order of mental labor: ie The best activities had to do with working with data or numbers; the 2nd best activities were things that required memorization (students, actors, speakers, etc.. The third best was getting out there and socializing, staying active mentally with friends. And the last, and most damaging was watching tv & building puzzles.
I would love to make it to 90, but only if I am coherent enough to enjoy it. I’m sure this decision won’t be my own, with the new deathcare coming into law. At this rate, we’ll be lucky to make it to 50.