Occasional bedwetting is not that unusual at that age. I used to babysit a lot as a teenager and I knew kids in at least 2 families with that problem. A good place to start is with a waterproof matress pad (one for the whole matress under the sheets and a small one over the sheet so you don't have to change the bed in the middle of the night). Next wake him up and take him to the bathroom after he has been asleep 60-90 minutes (or right before you go to sleep). You don't have to talk to him, just guide him to the bathroom.