My Father started me shooting when I was 6 years old with a .22 rifle. It sounds like you are looking for a deer hunting rifle. Most of the rifle stocks out there will not fit your son,they are made for adults. Now there are youth models being made these days that might fit him,you will have to go to a gun shop and see. There is not much recoil from a 243,if and adult is shooting the rifle. Not knowing your son I can't say if he could handle the recoil. Find some one you know that owns a 243 and take your son to a range and see if he can stand the recoil,it may well be to much for him.