Well, great. Certain "overachieving" students might even use Time-Turners take an impossible number, ala Hermione in her third year... Maybe older students would be able to handle it better than she did?
Another thought I had when I read Tatsua and DAWNSTAR's posts just now was that the school could actually be something of a combination of secondary and post-secondary... What I mean is, it could go two years past the traditional American 12th grade, and graduating from Kingsridge could be equivalent to an associate's/two-year college degree, or something like that. It would definitely help to differentiate and codify the teaching style, and would help to make a better case for the curriculum I proposed above.
In the final two post-secondary years, I'm thinking that each student focuses heavily on their personal "core", and at the end they provide some kind of proof of excellence (a test or whatever) that allows them to graduate with full recognition in those fields, in addition to the blanket recognition from simply graduating in the first place.
Does that make sense?
EDIT: If this was put into place, it might give us a larger range of ages, as well, because some players might want their characters to be in those two final years instead of the earlier four. :) Just a thought.