I wouldn't buy a Spyder if I were you. Decent starter bow, but doesn't leave enough room for draw length adjustment when he grows.

As for weight? Tough one for anybody that age. I'd recommend taking him to a proshop and see how they fit him up. Hands on is probably better than us guessing anyway.

I know as he learns how to draw and shoot he'll be able to draw more weight. But till that time he needs to be able to draw and hold, learn how to develop some sort of shooting form. This can't be done if struggling with a bow.

There are a couple companies, Parker for one,that make bows for kids and smaller statured people that for a nominal fee (around $50) the bow can be fitted with heavier limbs down the road. I'm sure there are a couple others, but I'm sure about Parker. So maybe start him out with a 30-40, which could be fudged down below 30# for a while. Then a couple years from now boost it up to 40-50 with new limbs. 50# should do the trick for several more years---when he can buy his own bow. haha