About 5 or 6 years ago, I hurt my right 50 yo knee (feels like under the kneecap but pain spreads when worse) during running football pass patterns with my son. It never bothered me enough to go to the doctor, but the tightness followed by pain would increase during hikes or walks longer than a couple of miles. Oddly, it didn't bother me much during cycling but I rarely ride for more than a couple of hours at a time and I rode for pleasure rather than a workout.
Well, since the problem wasn't going away and in fact getting slowly worse, I started a training program about a year ago that consists of slowly ramping-up distances and efforts of BOTH walking/jogging and cycling NO MORE than every other day. I try and do only stretches on the off days. I believe my current almost complete lack of knee pain during my proscribed workouts are a result of this cross-training followed by stretching rest days. One thing I also do, when the knee starts to feel "funny" (which happens before it starts to hurt) I cease "workout" and coast or limp home. I may have read someplace that working thru the pain is the worse thing you can do (its ok for "no pain no gain" muscle-building but not for past middle-age joints and ligaments). I might add that I am HWP and have always been in relative good health. Anecdotal evidence admittedly but it's helped me generally and my knee specifically.