Dear Not Sure Which Way to Go…
YA fiction does have its 18-year-old characters, some even graduated, so characters’ ages aren’t your determining factor. And YA does have edgy content. The agent’s suggestion that your plot and maybe even concept are better suited for the NA market is illuminating. Ponder a third factor: your characters’ mindset. Each developmental phase of life has a general sensibility, or way of processing the world and one’s place in it. Do your characters seem to be processing the greater world for the first time, figuring out how they fit into it? That’s very teen. Or do they have enough life experience under their belts that they think they’ve figured it out, at least a bit? That’s a general trait of new adults, who then explore and advance their world views. NA stories force new adults to reassess what they thought they knew as they fight their battles. Sometimes they confirm what they’d figured out, but usually they’re breaking down and rebuilding. If that sounds like your characters, and your story’s circumstances feel far enough out of the teen realm to send up flags with an agent, it’s likely this is an NA.