My Dad and Mom let me go afield alone with the 22 rifle when I was 9, and with the 300 Savage when I was 12. I was 12 when I got my own handgun, a 51 Colt Navy.
However I grew up without many playmates of my own age, so my friends were my dad's friends, all adults, all WW2 vets and all very safe in their gun handling. It was a treat for me when his friends would come over. Most of the time I was alone except for my dog.
We were outside of a town of only 3,800 people about 9 miles, so the whole mountain range was my shooting range and play-ground. Our nearest neighbor was about 200 yards away, but our second-nearest neighbor was about 2 miles away.
I am now 58. Just last week I had to deal with a man in one of my classes who is now 74 years old, and he was still not “old enough" to have a gun in his hands without supervision.
So I am of the opinion that it depends on the individual, and the level of training he or she has.
Allowing kids to play with toy guns like they are toys means you have to train them to NOT do things later.
Only allowing kids to play with toy guns as if they were real means you never have to teach them a different way to handle a gun.
My dad was a vey wise man.