Can someone spell out to me exactly what I need to do to fend off old age?

Take vitamin D 10mcg daily.
Wear SPF 50 on face and neck daily. I like Eucerin oil control, it doesn't feel anything like sticky sunscreen.
Many areas offer 12 week free gym memberships and training with a GP referral, could you try that? In my area you need the slimmest of reasons to be eligible eg back pain, who doesn't get that sometimes. My surgery has a health and wellbeing team who offer coaching for exactly the kind of thing you're asking about, might be worth asking yours if they have this service.

No or low alcohol consumption is good, get a good BMI, beware fat around the belly. Don’t worry about low fat, worry about eating too much sugar and also look at what oils you eat. I have a condition which means I get chronic pain, it’s a congenital issue that worsens with age and there is not much I can do about it. But in my mid fifties I can still hike for 10 miles and DH still runs a good time for 5k, I can’t run anymore due to my congenital spinal defect. We have never been overweight. Eat as little ultra processed food as possible. I still walk for a full hour most days even when in pain and do stretches, though I have an ear infection currently which is being treated and am a bit whoozy and off balance so can’t.

Yoga or something similar (to stay supple), resistance exercise (e.g., weights) to maintain muscle (we lose muscle as we age) and healthy food. Maybe ask your GP for a blood test to make sure you don't have any vitamin or iron deficiencies. Sleep on a regular schedule (there are certain processes that happen in our bodies on a schedule and it goes haywire when we miss out on sleep).

Get on YouTube and check out Joe Wicks's workouts. They don't require expensive equipment and are well-organized so that you'll be targeting important muscles. You can do things like squats while waiting for the kettle to boil, for example.

Also get regular dental check-ups. It'll be worth it. I need to take my own advice there.

I think it's because people in wealthier areas in the US do all this that they look so healthy.

Good luck.

https://youtube.com/@fabulous50s?feature=shared

See what you think of these videos ^