When I was 17 YO, I was issued a select fire M16A1 rifle and trained in its use. I was also trained to operate .50 caliber Browning and M60 machine guns. I knew how to kill grown men using anything from my bare hands to a 16 inch naval gun (if I had the right radio). Yet, I could not go to the E club and legally buy a beer. I also couldn't go to the PX and purchase a firearm. I actually became a marksmanship instructor before I reached the age where I could legally purchase a firearm...
Same here, but we had M16A2s to train on. Couldn't buy a pack of smokes, but we'll train you to kill.