Yes sign him up. Seek out a recreational league that guarantee's that all kids play. He may not get time at pitcher/catcher/FB unless he shows some ability but that's also a good thing for safety. At 9-10 the more experienced boys are hitting pretty hard and throwing in the 40+ mph range.
Baseball has been great for our family though we have experienced some real negative times as well (I have posted in OT about them). Lots of the "daddy ball" syndrome and super competitive parents/coaches. Try to minimize that with your son(s) and focus on keeping it all fun and definitely enjoy the time out in the backyard throwing with them. Good times
