I used to let DS5 go to bed whenever he wanted. Historically that was sometimes as late as 3 a.m. on a school night (he was miserable the next day). Midnight is nothing to him, except perhaps an excuse for a late lunch. We've recently started enforcing a 10:30 p.m. bedtime on school nights; I know it's not much, but it's a start. He usually reads in bed for a while after that. He has been less grouchy after getting to bed around that time, although he'll probably never be a morning person. In our case it's not that DS5 needs less sleep, but that he just doesn't like going to sleep much.
I wouldn't personally take books away from your son, since it sounds like he's doing all right. I know that reading can keep one awake, but it's still a physically passive activity that can also help one relax, and in the meantime your son will get hours of extra learning each week when he might just wind up staring at the ceiling otherwise. If it ain't broke, don't fix it. Your son might just need a lot less sleep than normal.
