The old Daisy Red Ryder is a good starter gun, not much power and very reliable. I think it's been a "first gun" more than all others combined. It's really just a "plinker" gun, short range and low velocity.
As he gets older and more responsible there are guns that are far more reliable and accurate. Some of the modern BB guns are extremely powerful and have tremendous distance, so you have to be careful where you shoot them. Some of these approach the small caliber rifles in power.