Another thing that really helps your knees is walking barefoot - OUTSIDE - for about 20 minutes every morning. It doesn't matter if you live in a city - your knees don't care. They just need to be allowed to move properly and they can't do that if your feet are imprisoned in boxes all the time.

You should start at just a few minutes and build up slowly. Walk backwards too. Go up hills and down hills. Do squats a few times a week and then spend 1 minute squatting properly with your feet flat on the floor. You might have to build up to that too - start by counting to ten in your squat or as near as you can get.

I've done martial arts all my life and my knees and hips are fine.

I'm 65.