"Knee problems" had the same problem for the past 6 years or so. Besides my age, it's probably due to all the years of going heavy on squats in the gym and working construction for most of my adult life.
Started taking a supplement called MSM along with vitamin C that is necessary in order to absorb the MSM. Literally over night I was able to do deep knee bends (no weight) without any pain.
After about 6 months of taking it religiously, my knees rarely hurt except on occasion after leg days in the gym.
I'm also on a regiment of vitamins and various supplements that has given me a new lease on life.