I had this same question after being surprised when I needed reading glasses and when single strands of mutant hair sprouted from various places (eyebrows, neck, etc). My parents passed when I was a young adult so I didn't have many older people around to ask about these kinds of topics.

You focused specifically on physical health. Others have given good advice (teeth, hearing, etc). I'd add several other points:

-- At around 50, your chances of getting cancer hit an inflection point on the "hockey stick" growth curve [1], so you need to get regular (annual) screenings. A good health plan is helpful; when I was on Kaiser HMO they were really good about following up on this.
[1] https://www.cancerresearchuk.org/health-professional/cancer-...

-- Exercise doesn't have to be intensive to work well. I rarely go to a gym now; when I was younger, the overhead of going to the gym made me think I had to workout for an hour or more, but in my case it backfired, bc it led to a gut reaction of "ugh" whenever I thought of the gym. I'm pretty committed to hiking, so now I walk outdoors (mineral sunscreen, of course) for an hour per day and that's enough. If you can choose to live somewhere where you can do this year-round then do it. That alone is transformative. When I first started hiking, my knees would hurt, especially going downhill, but after a few painful hikes, it eased up and now many years later my knees never bother me.

-- Highly-suggested weight training books (e.g. Starting Strength) insist on free weights, barbells. I find that 30 min of body weight circuits (and dumbbells) 3x/wk is plenty. Just get into the habit. The benefits accrue over time, whereas you'll see peers your age or younger neglect this and that neglect also accrues over time. Most people don't add 25 lbs of belly fat in one year, it's more like 2-5 lbs per year over decades.

-- Most my friends are younger than me and alcohol is still a big part of socializing, but as I get older I dislike the effects more. Not that I drank much in the first place, but now I've cut back even more. On average not even once per month, and never more than 2 drinks per occasion.

-- Diet is obviously important. Michael Pollan's advice: "Eat food. Not too much. Mostly plants." I still eat too much meat but include greens in every meal. My advice is to cook. As I got older I started cooking at home more. Over the course of a decade I eventually worked up to cooking every meal at home. It helps to establish the habit if you have someone (spouse, family) to cook for, but now I have the habit, it's easy to cook for myself. When you cook, you can eliminate added sugar. All processed food has sugar in it, so I cook everything from scratch. It sounds like a pain, and when I was younger I would never have imagined myself doing it, but when you practice it, you can do it quickly. I eliminated sugar on weekdays. If you follow David Sinclair's longevity advice, you'd cut out sugar entirely, but I still partake on weekends.

-- So far I've been super lucky and have no major health issues/struggles. I'm "old", but not elderly. I still do long distance treks. People I meet are always surprised at my age and energy level. The biggest tell is white hair, or dry scraggly hair. I used to think I'd be interested to hear health issues from people in the 70-90 age range, but I suspect it's so different for everyone that it wouldn't be that useful. I believe there's enough longevity advice out there that if you pay attention to the right sources then you can see what's coming up and what you should be doing.