Where does YA end and Commercial Fiction begin?

Okay. So I wrote a book about a pretty sensitive topic that I hope to publish. But I'm torn over what genre it falls into.

The main characters are teenagers whose love spirals dangerously out of control making for some pretty strong subject matter. It's loaded with drinking, drugs and very grown up choices. Bad language, lots of not graphic sex (hey, they're teenagers) and plenty of violence.

But here's the thing. The story takes place in the 1980's. That's right. The era of Member's Only jackets and Vans (the first time they were popular). It's spotted with muscle cars and real rock and roll that today's youth wouldn't particularly care for. Or even understand for that matter. There were no cell phones or ipods. There were however, rotary phones and cassette tapes.

While the language isn't terrible, when it's bad, it's bad. Which leads me to my next question.

Are book genres like movie ratings? Does saying the F word more than once constitute an R rating?

And like I said earlier, the sex itself isn't graphic, but the emotions that go along with it are.

I'll admit that it's not something that I'd be thrilled about my 17 year old reading. It's too much.

On a side note, I received 2 rejections yesterday. One agent said that my writing was solid and it deals with a  very important subject for women to read. The other said that she read my manuscript with great interest. They both said they were afraid that they weren't the right agent for this project.

What does that even mean?!

So I ask again. Where does YA end and Commercial Fiction begin?