check out a mathews mission craze...bought one for the girl friend....goes from 15 to 70 lbs and 19 to 30 inch draw so it can grow as he grows...pretty short limb to limb and very light...havent shot it through a chronograph but it seems to be hummin em pretty dang fast at 39#s and 23 inch draw
I have a Barnett vortex that he can grow with brand new bought this year for my wife completely setup ready to shoot all adjustable 19-45 lb pull all different lengths different cam pieces to adjust it. 200 bucks 4783575498
However, if you don't want to spend a lot of cash until you know he'll stick with it consider the Bear Scout. I have two sons, a lefty and righty so I think Santa is bringing two of the Scouts. Now if they stick with Archery, and the bow doesn't end up in a pile with all their other "I wanna" stuff, then I'll invest in a quality bow later.
What ever brand or style of bow that is chosen, choose a lower draw weight. As the young archer progresses, age wise and strength, this draw weight can gradually be increased. Check out a Pro Shop as they have knowledgeable staff and some shops even have a small archery range indoors or out to help the young archer. Too heavy of a draw weight for anyone, where they are basically fighting to get a bow to full draw can: 1)damage muscles or tendons, 2)cause a person who could enjoy archery to either give up all together or shoot less than what they had hoped for. Best of luck.