I'm 41 and have been doing the jits for 7-8 years. Even had aspirations to get in the cage a few years ago, but found that it was keeping me from getting sleep, which meant I couldn't function in my day job. Lame, I know but it is what it is.
These days, I've taken a lot of time off. I seem to get hurt way too easily lately. The last time I went in, it was the MMA class and all we did was throw jabs and counters (slipping, bobbing, finish with some combo). My lead shoulder took a good couple of weeks to feel better after that. A month ago, I tore my calf muscle playing soccer. A while ago I tore my pectoral trying to finish a low single - a move I've done a thousand times, but this time it popped. I'm starting to think I may be at the age where combat sports might not be a good idea any more.
I would add though - I was a HS and college wrestler so my body has a lot of wear and tear to start with.