I made a wooden rifle for my son when he was two. He had to follow all of the gun safety rules with it. If they can pay attention to the rules when "playing" by themselves, they will probably be ready to be immediately supervised with a real firearm.
And there we have it. My kid was not ready at two for even a toy gun yet here is another kid who was. It's all a case by case basis determined by the parent. Parents make bad decisions sometimes sure but I'll trust a parent until they prove me wrong before I'll trust a blanket statement applying to every kid.
I agree completely, my brother, at 52 still shouldn't be allowed to have a gun....
BTW, my son was making everything into a gun so I figured it was time to teach him the rules. They also included not touching real guns. That was why I made a wooden one, all of the toy guns were, IMO, too similar to real guns for a two year old to differentiate.
We had some raccoon issues with our chickens and had an unloaded shotgun by the door. About six months after getting his wooden gun, I happened to see him walk over toward it and was curious what he would do. He did not know I was watching from the balcony as he stepped next to it, looked it up and down, started to reach for it and then yanked his hand back when he remembered what he had been taught.