I wouldn't suggest a pump though. Well, not unless he is the son of Arnie
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To be honest, there's no better way for him to learn the key points of the game. If he has physical issues with pumping the marker, post up here, and we may be able to help you change it.
If you can find him a pump, then i'd make sure to drill the safety aspect into him as early as you can. Once you have that nailed, you can go crazy on technique, but i'd make sure he knows the dangers and consequences of his actions VERY well at the age he is at the moment.
For reference, the age restriction for publics sites is 12+.