What ChaseJxyz said.
You need to figure out which target audience you're appealing to. (Not the only audience, but the place it would stand in the bookstore, that people would most likely look to find it.) The narrator age is not the sole indicator; there are adult books where the narrator is a child, but that doesn't mean you'd hand Room to your five-year-old. It's about subject matter and tone.
Have you run your novel past any betas? What do they think it reads like?
If all else fails, what are your comp titles? What's their target? Start with that.
(Also, YA/adult is not a genre, it's an age category. There is YA mystery, YA fantasy, YA historical, YA romance...)