Iwan, I agree generally, except that 85 and even 90 are a bit too young. I know people in their late nineties who are too creative, active and alive to begin giving up. Not that giving up is not alright, especially when ill.
JLNobody, you're right, but I was using 85 or 90 as a general point of reference. My family has a history of longevity, with five living generations in my lifetime until only a few years ago. And this was not accomplished by giving birth during the teen years, but near or after age 21.
My grandmother died "young" at 98 and was active and healthy up until near the time of her death. She was around for most of the 20th century and proclaimed that television and the microwave were, in her opinion, the greatest inventions of the century.
But, the point is . . . she became bored and simply tired of living. Would she have wanted to live longer if she looked and felt younger? I don't know, but I really don't think so. And, if science-fiction movies are an indication of the lifestyle of the future - no plants, trees or open spaces, living in cubicles, nutrition from tubes - I'm not interested.
Living "forever" is not the object of slowing the ageing process; however, even if people could live much longer, healthier, and youthful lives, eventually, both the birth rate and the death rate would be highly-regulated . . . i.e., you'll have a specific time for both your arrival and your departure. Otherwise?????