There are a number of factors, but one thing I did when I was 17 was a stupid move. Long story short, I flipped a car, end for end, twice. This screwed up my back which as I got older got worse and worse to the point where at times (like yesterday) it can flare up and make walking any non-trivial distance difficult and painful. Beyond that, if I try to do certain kinds of physical exertion, then my back and neck make that difficult too - so combine that with the fact that I am a bit lazy, yes, my lifestyle is more sedentary than is healthy.
If I had stuck with physical work I would not have made it this far because of my back. I have a friend same age as I am, who did physical work all his life. He wore out his knees and has other physical problems now and had to retire early several years ago.
I do not have the best genetics either - no one in my immediate family has made it past the middle 80s before dying of cancer, stroke or heart disease. My father was fairly physical - he hunted and exercised regularly up until the last couple of years and died of cancer (recurring) in his late 70s (also had dementia and other related issues). I had an aunt who always seemed very healthy and led a healthy lifestyle who suddenly died early in her 70s from an intestinal issue.
Stuff happens - deal with it.
Been there . Also riding the old dirt bikes of the 60,s that weighed a ton and had 3 inches of suspension travel.After I got older I ate tons of Ibuprofen To deal with the arthritis That found a home in all my old injury's And joints . Ended up with bleeding ulcers of coarse. But I know guys that sit behind a desk that did not make it this far. Maybe its conditioning , like boot camp . If i keep moving it seems to be better and if i dont let myself get over weight helps.. A extra 30 pounds makes a big difference on the knees and low back. They should introduce a automatic right to stand your ground law for guys over 50. If things get ugly I sure cant run very far . LOL