When is a child old enough to use a gun responsibly?
Never, according to the American Academy of Pediatrics. ....No matter how much instruction you may give him or her, a youngster in the middle years is not mature and responsible enough to handle a potentially lethal weapon.....
So.... take away the baseball bat (and ball for that matter), steak knife, car, bicycle, swimming pool, anything electrical, most household cleaners, lawn equipment. What have I forgotten? Oh yeah, educate your kids on all the above and let them use them appropriately and appropriately supervised. Including firearms.