I don't know if I can speak much to his high school years. He left our school after his sophomore year for a school (Notre Dame) with a better reputation for getting kids into the D-1 schools. I do remember him coming in as a 14 year old kid. He was already 6'3 and something like 230 pounds and was benching a lot more than many of the 18 year old seniors. As a freshman, he was a really good player, but you could tell that he was hesitant at times (probably because he was relatively new to the game). But he definitely got better as the season went on, and well for the rest of his High School career...he pretty much dominated.
On his personality though, a couple of things stick in my mind.
1. Extremely loyal to his teammates
2. A very polite kid, always said hi and waved to my parents when he'd see them
3. Just a really funny guy
Also, he comes from a really good family
ESPN Article
Couple of other things I remembered:
He was a vocal leader on our team as a freshman
Once (and only once) I beat him on a drill (even I was surprised). You could tell he was disappointed in himself and basically went ALL OUT the rest of practice. I just remembered getting clobbered by him on the rest of the drills for that day. He hates losing.