I'm now 51 and was really good in tournaments till I blew my knee out 3 times at age 40, 42, and 48. I've pretty much given up hope of doing a lot of things I used to do but I now know my limitations. I understand my kicking is going to be dodgy at best due to my lack of mobility, but my strikes are still pretty darn good. I train on my own when I can knowing that I'm only going to get worse and worse over time. But as long as I enjoy it and know my limitations, I think any martial art is better than no martial art even though being a third dan now means a lot less than it used to.