How will he play with his friends. Can one enjoy winning when no one wants to play?
This is why he must develop good sportsmanship, because nobody will want to play games with him... especially if he is a braggadocios winner.
And, if he is truly beating everyone at everything, I'd strongly suggest seeking out more accomplished players -- who can whoop his skinny butt -- so that he doesn't get overly confident, and stands a much better chance at improving.
For chess in particular, get thee to a chess club! In person would be best in terms of developing manners, but on-line would definitely take care of the challenge and enrichment.
It won't take too many whoopings to give him a good sense of reality.
One thing an organization like DYS will do is get him around his intellectual peers... I imagine it will be a whole new ball game. I'd bet that no matter how smart our little rocket scientists seem to us, on day one @ a DYS-type gathering, we're gonna meet the kids who were doing differential calculus before they were potty-trained. Kinda puts everything into perspective in a hurry.
