I'd like to bring out the cattle prod (we had one when I was a kid; it was for the dog, and didn't work on him either), but I can remember my own youthful self lying in bed pondering the mysteries of the universe (like why I would choke if I ate english muffins in bed) or making up stories in which I was usually some kind of spy, or imagining pictures on the ceiling and calling it television. (We didn't have a set till I was in 2nd or third grade, so what did I know, except for the name?) And I can't really disapprove of him reading, of all the things he might do.
Mostly, as long as he's not bothering anyone else it's not a big deal. But perhaps that's where my resentment ultimately comes from: on any given night when B has been up at midnight, 230 and 5, I would like nothing more than to collapse into bed after C has had his bath and gotten his pj's on. But I'm damned if I can go to bed while my four-year-old is still up and chipper.