This is why god made single shot 410's! The slugs will take deer to 35-40 yds. He will outgrow it in a couple years, then you can play with it a few years, then later he we appreciate the challenge of hunting with one. I say a single shot 410 first and a semi 12 when he is about 13-14.

edit, this in addition to a 22, he needs to be a good rifleman too!