How do I define my book?

I’ve started writing a post apocalyptic novel set twenty years from now in a post economic world. When the time comes to target agents, I want a solid understanding of its genre. I came across a previous post written a year ago or so by an older writer who penned a dystopia but their characters were older, and did not really fit in the YA arena. They were having issues defining their book.

Now I am too. My two MCs are 20 years old. There is no swearing in the book, just gentle kissing. But there is sex scene (not described, just mentioned) At first I was going to sell it as a dystopia/speculative fiction but now not so sure. I’m wondering if it would be better suited as an Sci Fi. I can’t make up my mind. What really defines those genres?

Mmm..You have both addressed good issues. In my novel, the US and European collapse (which is not so far from the truth if you think about it) plunging the world back a hundred years. People live in colonies. A global riot stripped the world of its resources. Im still writing it so I will most definitely change some things during the editing process. If I find I am not getting any bites with my 20 year MCs, I will most likely drop their ages.
Thanks for the help, guys

Thanks, triceretops. It's nice to know there is someone out there with the same thinking. Im sure there are NA Dys out there too. I hope so!