I used to subscribe to the idea of him being a mad genius. Now I'm inclined to say sublimely talented and pathetic. Bottom line, he's not smart enough to realize he could grow up if he tried. Or maybe he doesn't have the cojones to do it.
It all begins and ends right here:
"...but also he truly seemed to expect from himself nothing less than perfection. He was and still is the only player in the game who gets ticked almost every single time he misses a shot. It is a trait he inherited not from his father but his mother Kay, who, when John Sr. came home years ago and announced he'd finished second in his class at Fordham Law, told him, "If you studied harder you would have been first."