It's quite possible that future science has determined that learning calculus is the easiest and most intuitive at that age, and grows more difficult in later years - much like certain century-old beliefs about teaching languages are currently challenged and earlier-is-better arguments put forth.
But future science might have found similar shortcuts to the learning of medicine or comparable fields. Or then it's simply a technology issue: rather than inefficient lectures, one gets the facts from interactive media - and needs much fewer facts (relatively or even absolutely) because the entire pool of facts is now available to one, pre-digested, through various expert programs and whatnot, and cramming it into one's brain would only be counterproductive.
Any good scifi ought to tackle the problems of general education in a world that offers way too much for any poor pupil's brain to cope with, and grows worse in that respect by the day. Should only absolutely necessary things be taught, tailored for each pupil so as not to overload him? Would novel education techniques help? Should no facts be taught at all, because the time would be much better spent teaching the pupil to learn by himself? Centralized classroom-style education obviously survives in Star Trek, but AFAWK only as a hobby project for the well-intentioned but potentially utterly incompetent Keiko O'Brien...