Never too early to begin the process.
My sons, now 39 & 41, were curious as soon as they saw me get the guns out to go shooting. I began answering their questions at a level they could understand and trying to impart the inherent dangers, also at their level of understanding. By the time they were 7 or 8, they were shooting handguns with very close hands-on supervision with muzzle awareness and finger off the trigger taught repetitively.
Always, guns and ammo were under lock and key separately with keys not kept either accessible or nearby.
I had this great idea at the time that play guns led to unsafe habits, so they were not allowed to have them. They found an old childhood doll of my wife's with bent arms, took the arms off and used them to play guns. So much for that theory. At that time there wasn't the proliferation of lookalike airsoft guns. I think they knew the difference as they always treated the real guns in a safe manner.
By the time they were young teens, I would have trusted them will full access, but the friends they brought home most likely had no training, so the locked up separately rule was always followed.
Both my sons are fathers now, as well as hunters and shooters. Both use combination gun safes and have excellent safety habits. Soon they will be teaching my grandchildren about guns, so the process begins anew.
Now about lookalike airsoft. I am vehemently opposed to holding firearm manufacturers liable for misuse of their products. However, I would fully support holding airsoft manufacturers both civilly and criminally liable for any death or injury where a child pointed one at an armed citizen or police officer in circumstances where the armed person could reasonably perceive a deadly threat. They are principally marketed to younger people, look identical to real guns, and the red tip is easily overlooked in a stressful situation. This is a foreseeable hazard and, although these incidents are rare, the tragedy far outweighs the rationale for making them look and feel real for a game.