Reading some of the other posts in this thread and symptoms of your own, I would recommend also seeing a chiropractor or kinesiologist. I'm not 50+ but I saw this thread scroll by on the iSpy feature and figured my own personal experience may be useful information to those who are experiencing a sequence of pain starting with ankles then knees then hips.

In my situation, I have very high foot arches. Because your typical off the shelf footwear doesn't account for proper support for my arches it was causing my foot to twist inward slightly. I was getting a clicking sound in my ankles, then eventually quite a sharp stabbing pain in my knees whenever I climbed stairs or any sort of hill climb on a hike. My hips were starting to get sore as well.

My chiropractor made some casts of my feet and the lab created some shoe inserts. Almost immediately the pains went away. Within a couple months there were no signs of there having been any problems.

I bring this up simply to point out that not all symptoms are necessarily the result of the same affliction that another person has. If you have the joint pain in your knees but nowhere else, it is likely some sort of mechanical error like mine, rather than disease such as arthritis.

It is a little more difficult in the US than in Canada (I live in both during different parts of the year) to get to see specialists but I certainly recommend pressing your doctor for thorough examination and references to see the proper professionals for your situation. If your insurance covers chiropractic it is well worth it since an insert that lasts 3 or 4 years is a little easier pill to swallow than a daily arthritis medication you may not need. Always research your symptoms and get multiple medical opionions, if at all possible. I hope you're able to pinpoint your pain cause and alleviate it and enjoy some good rides. See you down the trail.