I spent 35 years in practice treating joint pain.
Sound advice from the DO. Probably the two most important points: listen to your body and daily exercise. Extremely important as we age.
Lots of stretching, keep it low impact, practice the ranges of motion for the large joints (hips, knees and shoulders) every day, add new routines as you improve.
One thing he didn't mention. For us oldies expect a little pain. 20 minute cold packs as needed helps, and modify your exercise when pain inevitably crops up. But, keep going!