If you’re involved with publishing at all, you know that the young adult market (YA, but I like words and not alphabet soup, remember) is jumping right now, most of it attributed to the successes of the Twilight and Harry Potter series. So publishers have been scrambling, I suppose in the last few years, to cater to the demand for young adult literature. I won’t inundate you with links, but there’s the Top 50 Young Adult Dystopian Novels and The Rise of Young Adult Dystopian Fiction, both dealing with books for a demographic that had to look up the word “dystopian”.
The idea of fiction tailored for young adults makes sense for publishers to adopt, but it’s really an arbitrary standard, I think based on the arbitrary standard of Westernized, state-sponsored education. You’re a teenager — technically, though it’s based on linguistics — when you turn 13. Then there’s four years of school, then you magically become an adult at 18, though still a teenager for two more years. You can gamble and be shipped off to war, but you can’t drink booze nor rent a car and get those hands off the high school students. It’s a dizzying complex of socio-political “rules” that don’t really coincide with nature. In more sane times, if you could bear children you were pretty much an adult, both culturally and in the literal sense.
My point in mentioning this is that I believe teenagers can mentally apprehend the same things adults can, but they’ve been socialized by a host of psychological rules, for good or bad, that have crept into educational systems and cultural modes. To this end, really, teenagers should be able to contextualized “adult” material in books just as well as “legal” adults can. I don’t know what is really that keeps Western/American teens from really achieving this; but my guess is that a lot of it is the ridiculously immense social pressure from all directions to just stick with the randomized, transitional period of life called adolescence.
And so we have this niche market that has exploded into something not as small as something we think of as a niche — this market that ncompasses teens up into maybe college-aged adults, with their own set of conventions and outlooks. I don’t believe this is top-down created by the publishing industry but it is in response to consumer demand, which is formed partly by social conventions. In reality I don’t think there should be much of a distinction between the things that adults read and the things teenagers read, if things were done “right” or “better” (whatever that means). I’m no psychologist or sociologist so take my opinion as highly amateur.