“What makes YA novels so popular nowadays with adults? And is the line between adult and YA fiction really there anymore, especially in fantasy and science fiction? I know that you aren’t a YA author, but with Nita, for example – is there a reason why your book couldn’t/wouldn’t be in a high school library? (other than perhaps sex scenes?)
As Cate said in the comments, the big determiner of YA is the age of the protagonist. A YA protagonist does not necessarily mean that the book is a YA, but an older protagonist pretty much means it isn’t. YA readers have too much adult PoV in their lives already; they want to read about people like them solving problems and making connections. The focus is also likely to be on different things. YA dystopias are different from adult dystopias; YA romantic conflicts are different from adult romantic conflicts. It reminds me of something somebody said about the difference between pop and country music: pop is about falling in love and country is about working on your second divorce. YA fiction is about becoming an adult and adult fiction is dealing with being an adult.
As for why they’re so popular, a lot of them are well-written and many of them are more imaginative and lively than adult fiction, possibly because their protagonists are still imaginative and lively, not beaten down by reality and the electric bill. And for adult readers, there may be the lure of reading about a simpler time (HA! Do you remember junior high?) before responsibility raised its ugly head. But basically, a zillion adults read the Harry Potter books because the Harry Potter books were good. Same for the rest of YA. A good story is a good story.
YA can have sex scenes; there’s a reason Judy Blume’s Forever will forever be a classic. YA readers want to know about sex, too, and since they’re having it earlier and earlier, they’re not nearly as innocent as many people would like to believe. What they are is clueless (something they have in common with many adults) about what sex can mean and what can happen to you both physically and emotionally if you’re cavalier about it. So if you’re writing sex in a YA, be very, very careful, because those young readers are taking cues from music videos and movies and TV shows and their equally clueless peers, and they’re primed for big mistakes; don’t be part of the problem. Don’t get moralistic or didactic, but be real, if for no other reason than disasterous sex is more fun to write than best-sex-ever sex.
And specifically, on Nita? If Nita and Nick were fifteen, the story could be a YA, but the sex scenes would be vastly different plus their freedom would be very limited as teens. At 33, Nita is pretty jaded about sex and at 529, Nick is remembering his long ago history as a playboy crook. Nita can also go anywhere anytime she wants, answering to nobody but her boss; if she were 15, she’d have curfews and be explaining things to Mitzi and the Mayor (her parents). Nick might have an easier time of it at fifteen, since in the terms of the plot he’d still be dead and his parents gone, but if he were a legitimately YA protagonist, he’d still only have the social and political experiences of a fifteen-year-old, so the whole Master of the Universe thing would be gone. YA stories are more about learning the world and taking control of it than already having that control and figuring out what to do with it, so I could write Nita as a YA, but it would be a very different book.
The key is, you really have to understand kids on their level to write a great YA, and then see that story world through their eyes, with their constraints and their lack of experience, while capturing the endless possibilities of youth. I couldn’t do it, even with fifteen years of public school teaching behind me. It’s a wonderful genre, but it’s really tough to do well.