I would consider something like the HR/NEF (or whatever name they currently go under), single shot, switchable barrel in .243 and .20 guage. The shotgun barrel can be used for birds, and upland game, whiile the .243 would be an excellent deer rifle. If it is to be used only for deer, you might want to consider a rifled barrel for the .20 guage, and let him shoot both (the .243 and the .20) to see which he is most comfortable with, as well as accuracy, range, kick, etc. Just try to avoid too much gun for a young shooter. He can always grow into something more powerful such as the 30.06. One word of caution about the switchable barrel .243/.20 guage, my son has one and loves it, but when target shooting, the .243 starts getting pretty erractic after several shots and the barrel warms up. Of course, as I frequently remind him. knock it down with the first shot, and fill the freezer.
It isn't what happens to us, it is how we deal with it, that matters most.