Find Your Cruise
I would make sure he takes hand held games consule incase ship hasn't enough for teenager to keep occupied except cinema theatre shows not likely to appeal.
Firstly, I thought children were meant to be back in school in January so I doubt if there will be any playmates for him on board at all. For a first cruise personally I would have picked one of the newer modern child-friendly ships but I guess it is a bit late now.
I agree with Aldrich, since children should be at school during term time you might not find many children on board but they do have a teen zone on the ship which is run by staff.