It's that way for some, to be sure, but it certainly isn't for others. My wife's family is long-lived, at least on her mother's side. Her mother lived to be 97 and we were disappointed that she didn't make it to 100, which a first cousin of hers did, and in pretty good shape, too.
I realize also that discussions like this are not things younger people (people in their 60s, for instance) want to read and others (not here) have mentioned that, too. Nevertheless, 'good health' is a relative thing, relative to, perhaps, expectations. Mental well-being need not have anything to do with age, which I say based on everyone I've ever known. If someone is a pain to be around when they're 40, they certainly won't be any different when they're 80. Physical strength is one thing; but physical abilities is something else. I guess I shouldn't go into that, however, but I'm not talking about skills.
From the more or less standpoint of this forum, I think the important thing, health-wise, is simply to keep physically active, as far as you are able, and naturally within the limitations of your circumstances. That's hardly a secret or anything knew but there sure is a lot of nonsense out there about it, mostly with the goal of selling someone something. So, get up and go take a hike. There is no danger involved, the cost is minimal and if you go by yourself, you go whenever you please, wherever you want and stay as long as you like. That phrase may need to be modified for those who are married, of course. Anyway, people were saying this more than a hundred years ago. A few things have changed since then, it goes without saying. There is less pollution in some places, especially in the cities, going somewhere is easier, and we don't seem to have the bad winters that everyone used to talk about. You don't even have to go to the woods, either, which are scarce in some places. Some cities have wonderful places for long walks, too, although you probably can't be nude.
The main thing is to live longer than Thoreau did, so you can laugh at everything he said.