I'll be 44 next month so I'm still relatively inexperienced with 'aging' in the decline-management sense but a few things that have been relevant:
1) My 30's nearly destroyed my health, I've been recovering, doing light workouts, and supplementing aggressively ever since (enzymes, collagen, vitamins, nootropic mushroom blends, autophagy supplements, etc.).
2) I like walking, it's low impact and keeps my legs in shape. For whatever reason I've noticed that while my legs are pretty large in terms of musculature I notice that my vascular health is touch and go - ie. if I stop walking for a week and try to walk a couple miles I'll be hobbling the first day I get back into it (maybe that will change eventually but for right now it's pretty standard).
3) Stretching and light weights - I do standing splits, touch my toes / ground for a minute several times per week and also have some light weights (again - rebuilding my shoulders). I'd like to get back into something like Vinyasa Yoga or finding a martial arts instructor who could hold a candle to the one I had for over a decade until last year.
4) Microdosing psychedelics - this combines with the mushroom supplements. If I understand Paul Stamets correctly he did some research into stacking a microdose of psilocybin mushroom with Lion's Mane and Niacin (B3) and that it had huge neurogenerative effects - I typically try to take Lion's Mane anytime I microdose.
5) Morning meditation - I do it every day, partly for grounding myself in the intention and purpose of self-reflection, self-improvement, and living my life (to the best of my ability) on the terms I want to live it - even if that means beating my head into the wall of spirituality just enough to keep my orientation out of pure materialist status-chase style living.
Fears?
1) If I end up living alone the big concern is having to deal with predatory dynamics from neighbors wherever I live (legal bullying, etc.).
2) I'm deeply hoping that I can invest my way out of the work world, or at least forced involvement with it. I want to stay busy and still contribute but with the understanding that the moment someone tells me that I need to do something illegal for them I know - at every level - that they need me more than I need them and I'd rather they knew that as well to avoid any confusion. The other obvious piece - being as economically and financially predatory as our culture is I don't want to be used, abused, and rendered homeless in old age - largely because people could care less about each other and would even care less about an autistic guy.
3) Somewhat like 1) but broader - I want to stay on top of how peer predation and bullying changes with age and I want to make sure that I know what I'm in for with respect to my 50's, 60's, 70's, etc. to see if I can get there pre-armed rather than needing a few years of massive trauma every decade of my life to force me to learn the new psychopathy format that my peer group has moved on to.
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The loneliest part of life: it's not just that no one is on your cloud, few can even see your cloud.