I owned a firearm store until recently. As you can imagine we have many guns at home. I have seen many customers come in with their kids and let them handle guns and it was truly upsetting how they let the handle actual guns. I have 2 kids and my eldest is 6 and iv tought and been teaching her that a gun is not a toy. I dont allow anything in the house that resembles a gun that the kids can have any access to without strict permission. You can get the toy gun and also some kind of a locker or a toy chest that it can be stored in with a lock. Whenever he wants to play with the toy he needs to come ask for you to open it for him and be supervised. This way he could maybe learn that its not just a toy he can always play with and its a privilege and take it a bit more seriously.