Stay engaged.
I don't do any formal exercise and am post menopausal. HRT was a boon. I also have rank osteoporosis and am heavily medicated for it (two broken vertebrae, a broken foot and broken wrist in the last 8 years).
I do gentle pilates, have a full time professional and stressful role, two grown up children, husband and home. I'm out of the house at 7.30am and back at 7.30pm. Sit too much at a desk but nevertheless much to-img and fro-ing to the copier, kitchen and loo. I manage about 3000 steps despite driving to work. I regard the big shop once a week as a mini work out :)
Add into the above, cooking dinner, running up and down stairs with laundry and to put stuff away and there's a reasonable level of activity. And the garden of course - a minimum of three hours a week, weather prevailing, we have half an acre.
DD and BF are constantly in and out and whilst technically she still lives at home, is only here for about two nights a week.
A big family lunch once a month, usually friends once a month, and trips to the theatre, dinners, etc., keep one active and socially engaged. Church on Sundays and commitments around that. We have a home in France and I still happily drive 700 miles with an overnight stop although more often now fly to Barcelona and get the train. At least 3/4 times a year. We sail when there and walk in the mountains.
I am 64, pass for 57/8, on the outside and in my heart am still 25. My bones are shit but I don't let them beat me and thankfully have a bit of stiffness but no pain.
It's a state of mind, good food, moderate alcohol and admittedly there's more maintenance - hair, skin, etc.
My mother is 88 and until she was 87 could do the splits. Like her I shall never stoop to an elasticated waist, polyester top, fleece jacket (beyond the garden) or velcro shoes.
Next year I'll retire and am looking into Trustee positions, school governor, etc., will join a book club and have a very clean house and an immaculate garden. Hopefully grandchildren will come along too.