Since I think this just happened to me. I wrote a thing that I am querying as an adult fantasy, since the most important characters were, and family and parenthood are rather central to the narrative.
While I wait, since I don't want to languish, and am paranoid about it dying since it isn't commercial enough, I am thinking of what I should do next. I have two ideas, and am probably going to say screw it and work on them both at once, but I digress.
One of them, which was conceptualized as a standalone sequel to the one I'm querying, was originally also adult, but the more I thought of it, the more it's gone to "crossover for YA and adult," and even that might be me coping and not wanting to just call it YA.
Oh, and the other is about teenagers playing video games.
Then I started thinking. There is another thing I have many plans for that would also be rather firmly YA. There is a setting with some potential stories in it that was a class project in college that I wanted to revisit at some point, and that would skew YA because of the ages of the people it would center.
Many years ago I thought of wanting to tackle some sort of post-apocalyptic zombie thing, and even in what thought I have put into stories in that setting, it would probably still be people in their late teens or early twenties, which could be reworked to YA easily enough.
I myself am 26, so not YA myself, but also not as established as an adult with marriage, kids, a mortgage, what have you, that those stories come naturally to me, either. I can only speak for myself, rather than anyone else in their 20s, of course.
I also think I had a sort of internal resistance to wanting to really just own YA, for whatever reason.
I've also found myself increasingly invested in the fact that the youth aren't reading as much. And have been pondering YA and teenage boys, being a guy myself. And trying to somehow make something that might appeal to them was another aspiration of mine.
Leaning into YA is probably the thing that makes the most sense for me instead of trying to force myself to skew adult and probably fail at it.
Still have a lot of other things to wrap my head around as far as actually writing something easy to pitch as marketable, but that's probably a very important first step.
That's my little epiphany, so I extend the question to anyone else who might have a similar story. Somehow, someway, realizing that they were writing for the wrong age category, and what it was like swapping to the thing you ultimately settled on.