1. You like good books more than you care what section of a bookstore they're found in or maintaining some ill-defined sort of lit cred (spoiler alert: it does not really exist).
2. You're interested in developing your own informed opinions about various genres and varieties of fiction. The lit cred of being actually well and widely read does exist.
3. Because YA is so powerful that it's built an enthusiastic reading culture all its own that includes both teens and adults, now in this our age of greatest distraction.
4. You've ever experienced something, anything for the first time, but especially one of those great big moments that help define or redefine who we are, that shape what we think and feel about love and death and life, those great big moments that change us or make us dig in deeper to who we already are. You want to feel that again. Or you want to understand it better. You want to understand what it's like for someone else. And guess what? These moments keep happening, your whole life.
5. You like stories that aren't afraid to put the experience of girls front and center, all different kinds of girls, and treat them as importantly as they deserve to be. (There are plenty of fine YA books starring boys and taking them seriously too, but I think we all know that finding those stories has never been a real problem, just a fake one.)
6. You like story. The pure, focused, raw stuff. It may be simple or it may be deceptively simple or it may be–oh yes it may be–complex, it may take place on a spaceship or in a mansion that houses a dark early American science experiment or in a high school, or in the future or in the past or right now. But you will have no trouble finding books that prize story, and there's no mistaking that. And story is one the most powerful substances in the world.
7. You're intrigued by the fact that while outsiders, aka those not well-read in YA, may try to pit fantasy and science fiction against realistic contemporary, humor against horror or girl books against boy books, most of the people in the YA community will tell you that's nonsense and that one of the best things YA brings to the reading experience is its ability to have all those things exist side by side, often within the same book, and to mix and match them with the freedom that comes from being a category more than a genre. A category that contains most genres and isn't afraid to push at the boundaries of them and of the category itself.
8. You crave an emotional journey and whether it's dark or swoony or light you can find an excellent example in YA.
9. You don't dismiss reader pleasure–not your own, not other people's. Whether it comes from delicious prose, unforgettable characters, strong voice or perfectly-executed twists, so many YA authors are masters at creating reader pleasure, while still telling whatever kind of story it is they mean to tell.
10. I could have really ended this list with number one, couldn't I? So the TL/DR is:
You like good books.