I trained in karate for about 6 years in my 20's and 30's, attained shodan and quit, then returned at age 54, to the same school. I am now 58 and 2nd kyu (had to start all over again, but that's fine). It's kind of strange, because muscle memory is so strong, so even when I first came back I could do a lot of the things I could do in the past, in spite of being very out of shape. This was good because I didn't have to learn everything from scratch, but bad because of muscle and joint stiffness. I had a lot of injuries in the first year, because I would get carried away and do things the way I used to, and would pull muscles and strain joints. I have mostly had rotator cuff injuries and elbow tendonitis, but a good PT and stretching and strengthening exercises have helped greatly. Now my big challenge is that I have developed some hip and lower back arthritis. Drat! It is frustrating, but I perservere. Fortunately, what helps it the most is a good workout! I have to be careful to warm up well, with some running and aerobic exercise, then good stretching, but once I do this and lose myself in just enjoying the training, I am fine. Surprisingly, my speed and reaction time are still pretty decent. It's just flexibility that is shot. Oh yeah, I get out of breath pretty fast, too. I'm just glad I can still play!