Knee problems can occur at any age, but pose an increasing risk as you get older because your bones, muscles and ligaments have taken years of wear and tear.

Exercises for weak knees should focus on stretching and working the muscles around the knee to help give it some extra support.  Those muscles are the calves, the hamstrings, the glutes, and the quads.

By strengthen the muscles, you can decrease the pain in your knees, as well as increase the amount of mobility you have in them.  

But if you experience any pain in doing these exercises, you should stop doing them immediately and consult your doctor.