Also, about the ages:
It won't matter that much how old they really are. They usually have older actors play younger parts anyway, expecially in teenage roles. Michael J. Fox played a 16 year old when he was 23 (or so). You really can't tell a difference on camera.
Remember, Snape is supposed to be about 36 didn't JK say and how old is Alan Rickman? About 57 if I recall. If people are going to complain about a big age difference, complain about that! hehe

- Bathazar Wulf.. yet again