For _me_, dealing with knee pain requires heavy squats and stretching. Sometimes it is mashing out knots from muscles where the knotted muscle is pulling on the knee in a bad way.
As others have said, it really depends on the person. Medical abnormalities can toss a huge wrench into this. In general, if you don't use it, you lose it. Do things that cause muscle to build and support joints and do some mobilizing/stretching.
Thanks for your feedback. Use them or lose them. So for <40 age we can do what you advised squats and stretching. But what about >40? please suggest.
Also I want to add https://superuser.com/a/914862 the first comment of the accepted answer tells other side of the story(out of memory stuff). This is just for the analogy. What do you suggest for that?
40, 50, 70... If you can move, try expanding your range of motion. If you can do the range of motion, start adding weight. I don't think there is something magic that stops one from starting to be healthier at 40. I'm also a layman.
As others have said, it really depends on the person. Medical abnormalities can toss a huge wrench into this. In general, if you don't use it, you lose it. Do things that cause muscle to build and support joints and do some mobilizing/stretching.