That theory really wouldn't make sense, as we refer to what the Americans call "junior high" as "secondary school" or "high school" (11-16). "College" as the term is used in the United Kingdom, also known as "sixth form", lasts two academic years (late 16 to early 18), within which period students take their A-Levels (usually), (supposedly) preparing them for university.
Addendum: I say "supposedly" because I really do not think it does, outside of the academic material. Most people that young, myself included, have no idea what they want to do with the rest of their lives, and due to an immature (physiologically speaking) prefrontal cortex, make poor life choices. It's no wonder so many people end up doing junk degrees, or never making use of their degree, often going into unrelated fields. Or indeed, all of those bachelor's pulling pints, steaming flat whites, and flipping burgers.