Eh, as someone previously mentioned, it's nothin' new. My mom had me at the age of 16, like tons of others such as myself.
Youth are pressured by ads and other forms of media that show attractive people "being sexy" and are usually accompanied by some form of words (mostly in ads and music) that attack their self esteem. Words like, "sexy, irresistable, lust, etc."
If a teen/adolecent happens to have low self esteem, sex is used to make them feel like the other kid reciecing it will like them more (in my own opinion). Although, it could also be one of those "the cool kids are doin' it why aren't I?" kind of things.
I dunno... I just know that I don't want my kid to grow up, cuz I really don't wanna relive my sex talk from my mom. LOL. Seriously though, I'd rather have my son make his own decisions and be safe about sex, if that's what he chooses to do, which means I'll have to talk to him about it.