If he’s 11 most plate carriers will bury him I’d imagine, a decent clone micro rig would have plenty of adjustability?
Room for 3-6 mags and pistol mags if needed? A PC isn’t going to do much to take the sting out of CQB IMO.
You might run into the same issue with the helmet / face mask combo, I’ve seen some younger players running around in some gear that would cause more harm than good.
Perhaps a dye mask? Decent all round protection so he won’t end up with missing teeth before his first girlfriend, look relatively cool and fairly breathable.