I figured out I was nonbinary in high school; it was generally just a gradual coming to terms with the fact that I never really fit with the category of "man" fully, but I experienced this dissonance as early as elementary, probably starting around 2nd-3rd grade. I'm AMAB, and while I had grown up with and admired male role models all my life (manifesting both IRL and in various fictional materials I grew up consuming), I never really saw myself for who I fundamentally was in any of them, at least not in whole. If anything, I resonated with the masculinity they projected rather than the male gender itself. As I learned more about what gender was as I aged, I learned more about different kinds of people whose presentation and expression didn't "match" their gender in the fashion typical of cisgender people. It was the gradual increase in my knowledge of gender that led me to realize that I didn't have to force myself to be a man to embrace my masculinity. I didn't have to put myself in one of two boxes; I could explore my masculinity on my own terms, and not under the internal presumption that I was a man. By being true to myself, I do so free of the expectations that society had placed on me by assuming I was male. And that's what being nonbinary has always kinda meant for me: being able to embrace my masculinity, my ambition, and my whole self without forcing myself into "manhood"; embodying healthy masculinity (the best I can lol) without living under the pressure to conform to what a man "should" be. I used to have some very absolutist beliefs about gender and sexuality that, thanks to both introspection and some conversations with friends, I've been able to challenge. Realizing that I was nonbinary wasn't just a mental awakening for me, but an intellectual one as well. Sorry this was such a late response, but I hope I was able to answer your question adequately ❤️