I recall seeing that the Australian novel Jasper Jones was awarded some literary prizes down under as a mainstream novel, but was issued in the U.S. as YA, perhaps for marketing reasons? It's written from the view of a teenager who gets caught up in the death of a classmate. I was just skimming a copy of Swamplandia, the award-winning novel from last year or so which is narrated in the first person by a 13-year-old girl. Maybe one of the differences is the Swamplandia narrator has the vocabulary and sensitivity of a 25-year-old English PhD. I'm currently reading Richard Ford's newly issued Canada, which will probably be nominated for a bunch of awards. The fifteen-year-old narrative POV is clearly filtered through the perspective of a man who is writing in his mature years. Likewise for Lorrie Moore's Gate at the Stairs, which has the patina of a first-person 19-year-old narrator, but has subtle clues that the narrator is now a mature English professor, hence the gorgeous language. This perspective issue is also why, to my mind, Prep is adult fiction, although set in a high school boarding school.