I picked up an old Chipmunk .22 for my 6 year old son and will be taking him to the range with it soon. He likes to go with me and watch but hasn't shot anything yet. He does enjoy shooting a Bear Goblin recurve bow in the backyard though. It is excellent bonding time.
Don't think it so much a "right from wrong" thing, but more of a follow the rules thing.
Some of us are still trying to understand "right from wrong" as it is.
To the OP, I started shooting a pellet gun when I was 4 or 5 yeas old. I could not hold the gun, so my dad would hold it for me and let me aim the gun by moving the forearm and he would allow me to pull the trigger. Think I was shooting at a beer can on the side of a hill at 5 yards back then. Incredible to think that this was in Kensington in Montgomery County. Probably get arrested nowadays for doing something like that.
I know for a fact that by the time I was in second grade I was using a .410 shotgun and that in 3rd grade I got the snot knocked out of me with the exposed hammer on the gun. Next day, my dad cut down the stock to the gun so I could actually put it on my shoulder instead of under my arm pit.