Strata (or: Salad Dressing)

I just had a thought, which may or may not sound slightly delusional and exaggerated, if you think clearly. And I shall proceed to tell you what it was, and ask for your opinions on the matter.

You think, when you're in high school, that you're all divided up into groups, that society couldn't possibly be any better segregated or more clearly cut into layers. That's before you hit college and the real world, and realize that the layers have been sifted off... people have settled into their strata, like salad dressing that eventually settles out into layers of vinagre, oils, and spices. In public school, you were surrounded by everyone. Every kind of person, or rather, every developing kind of person, was, at some point, in your vicinity. You encountered all types of people, without even trying. Once you hit the end of high-school, however, the sifting begins. College applications act as the first sieve. Universities separate people out by academic achievement (a.k.a.: motivated people, smart people, and people who just know how to suck up), athletic achievement, personality type, etc. Then you go through four years, give or take, with your peers (your kind of people) and you all sort of morph and mesh into one another. This is what we call "discovering yourself" in college. Is it possible that college isn't so much about self-discovery as it's about better fitting yourself into the mold of your strata?
I imagine that the next sieve is job applications and grad school. 'Cause once you hit thirty, you're pretty much settled, as far as I can tell. Once there, it's very difficult, rather uncomfortable, and definitely awkward to move outside of your group. I'm hard pressed to define exactly what these groups are - after all, this thought just came to me about 5 minutes ago.
I shall continue to puzzle it out, and get back to you on it.
for now... over 'n out.
E.O.