Ok, when we see James doing his exam he is probably 16- odds are that he has had his birthday already.
ANYWAY>>>>>>
What a childish bully he is! His treatment of Snape was done to amuse his gang- Sirius and Peter, and that is the worst for of Bullying. The way he talked to young Lilly was bad, too- " I'll stop teasing him if you go out with me... "
Very childish!
And consider how Harry taunts Dudley- he calls him Big D and diddykins (or whatever)- Harry is actually mocking his cousin quite badly. Still, Harry isn't performing for an audience, and so it's not as bad.
Still, it would appear that both senior and junior Potter's have a teasing streak, and are uncomfortable with women- look at Harry and Cho.