Your age is certainly not a factor. I'm a lot older than you and I know quite a few others who are and we often do dual system HS Varsity/JV doubleheaders. Get a physical and do some pre-season running. If these are HS age players, you will run a lot, so conditioning is important. It is more demanding than a night of SP, although on your feet that long and by yourself in one-pitch is comparable except for the distance at one shot.
You said you've taken a beating over the years, but again a physical and some running will tell you if you can handle it. It is an easy sport to learn the basics, but I would recommend attending some kind of clinic even if you have to go a distance for it.
This forum gets very little participation compared to the NFHS forum
http://www.nfhs.org/scriptcontent/va...f=14&submit=Go