To be fair there is a big difference. I went in the Army when I was 17. I was still a kid. I learned how to fire the M-16 in Basic Training at Ft. Knox, KY. Then went to Infantry training at Ft. Polk, Louisiana.. There I learned a bunch of different weapons systems. Before that, I had never touched a weapon, other than a BB gun. I did learn to respect weapons and what they could do to you and weapon safety, etc.
Having a kid who has no training just go and buy a weapon and ammo is dangerous. Perhaps a mandatory psych check, back ground check and weapons training before being allowed to purchase. Also a waiting period.