I didn't realize this until a couple of years ago (in my 40s) but boy did it alter my perspective on life. And I've heard what you're saying here from a couple other people in their 60s too. When you're young you don't really think about it much, health comes for "free."
But as you age your biology will force a choice upon you, one option is you spend progressively more time maintaining your health, in which case it drops off MUCH less than you'd expect. Or you can neglect that maintenance, in which case your quality of life WILL drop off in a big way due to health problems.
That's what it is, it's a choice, one you don't get to opt out of, but there is a path where you're in remarkably good shape for less effort than you would probably assume... for most people even just 2-3 hours a week of moderate exercise at the gym is probably a game changer.
I'm a little worried about the health of younger people today, because I read the statistics about obesity, blood pressure, ED and so on all going up for them. I'm also occasionally taking 20-30 minute walks with people in their 20s, who want to take a car, they're exhausted at the end of it, and they can't keep up with me. I get it, I was like that a couple years ago before I started hitting the gym, but really, at 25, you can't handle under a half hour of brisk walking? Oof, habits sure have changed.