I would recommend sticking with a .243. You already KNOW he can handle the recoil, and it's plenty enough gun for deer (it's also been used successfully for much bigger game although not recommended for that). Stay away from the .308, it just might be too much gun for the youngster. Keep in mind that as recoil increases, accuracy decreases even for experienced shooters. One of the things that makes the .243 such an effective gun is that it's relatively mild on the shoulder and therefor controlable/accurate. Whatever you get, if recoil is any concern, put a good pad on the stock - something like a Limbsaver or Kick-eez.