Good lord, actors play older and younger all the time- why would it be any different here? At this point, it would be more disastrous to try and replace any of the main characters. So far, they have made four movies in the space of as many years. The actors are all roughly the age of their characters as a result. They have three to go, and I don't see why they can't continue on as they have been doing. Daniel Radcliffe begins filming The Order of the Pheonix early next year, at the advanced age of 16. His character will be 15, and quite annoying. You may want to skip that one, Alex.
