Textbook version: unused muscle mass tends to decline gradually with age if nothing pushes back against it (sarcopenia, if you want the proper term) — plain English version: bodies don't fall apart with age so much as they stop being asked to do anything. Resistance training is one of the few things that reliably interrupts this, joints included: stronger muscle around a joint takes load off the joint itself, which is close to the opposite of what a lot of over-50s assume about lifting weights.
This builder puts together a free plan around that idea: a "Hypertrophy" or "Endurance" focus, up to 3 sessions a week, bodyweight or whatever light equipment you've got, over a 4-week block, with room to progress at your own pace rather than a 20-year-old's. Recovery matters more here, so don't be shy about an extra rest day if a session left you sore. And a plain caveat: if you're new to training or manage a health condition, check with your doctor before starting — this builds workouts, not medical advice. Just try it and set your days.