For a youth to be comfortable shooting, he needs a gun that fits him, not a gun already in our gun safe adapted to a much smaller frame. Check out the Mossberg 500 Super Bantam. It comes in 20 guage and will fire 2 3/4 and 3 inch shells. The best thing about it is the stock has spacer blocks to shorten the LOP and can be added back as the youth grows. A friend of mine bought one for his 9 year old and he is 11 now and it is growing with him. He shoots it extremely well and is confident with it but the best thing, it fits him. A couple of other things that will help is start with low recoil loads so they don't develop a flinch and make sure they wear double hearing protection when shooting so they don't flinch from the sound. Start him slow and he'll grow to love shooting.