This piece for Malachain collects the advice that holds up in practice.
Two short sessions a week of basic strength work protect bone density, balance and metabolism at every age, and the gains show within a month. The essentials are a squat, a hinge, a push, a pull and a carry: five movements that cover the whole body and can be done with a pair of dumbbells, resistance bands or, at first, just body weight.
Keep a notebook and add a little weight or a repetition whenever the last set felt comfortable. That gradual increase is the entire method. Rest a day between sessions, eat some protein with each meal and expect mild soreness in the first fortnight. People who stick with this for a year report easier stairs, better sleep and a quiet confidence that follows them off the mat.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.