Martial arts can be a fantastic skill to learn, for a variety of reasons. Age shouldn't dissuade you from getting back into the practice. I'm almost 40 and still practice most of my training. My parents are over 70 and they still practice as well. Over the years I've studied kenpo karate, tae kwon do, north american boxing, brazilian jiu jitsu, and kenjutsu - but my primary focus eventually became filipino and indonesian arts like pencak silat, kali, and kun-tao. It's helped, and continues to help, my concentration, coordination, confidence, spatial awareness, discipline, anxiety, and been good for my physical health as well. For me, doing stick-work or knife-work flow drills is almost meditative.