Personally, i think you should have bought 2 BB guns!!! Then go out to shoot yours regularly, and invite him to take his out too. That way, he see's that age is NOT a factor in BB gun shooting, and has "dad" to shoot against!!

I blow up baloons with my air compressor big, so they pop easily, and shoot at them with the kids. They really like to see them pop! BUT, don't stand close, as a tuff baloon will bounce a BB off it!! When he gets better let the wind blow the baloons around as you both shoot at them!!!

Drilling Man