Back when I was 8, I wanted to be just like my dad (before finding out his actual personality). I wanted to have the bodily characteristics of an AMAB person if that makes sense, IDK how to word it. I wanted to be mistaken for a boy, do the stereotypical boy things, reject makeup and dresses, and I went through a “girls stink” phase like some young boys did. I wanted my hair cut short because it made me look like a boy and even wanted to wear my dad’s clothes simply because they were “men’s clothes”.
“Girl" didn’t feel right to me but growing up in a certain kind of family, all I knew was the word “tomboy”, so I used that. But my family tried to convince me I was the most feminine girly girl, and that just wasn’t me. It felt wrong.
If you grew up to be a man, it might make sense to describe your younger self as a boy. My understanding of gender is that often the one you end up with as an adult is the one you really have had the whole time, or at least since you started having one at all.
But my other understanding of gender is that being in gender trouble is a fake idea, so you can and should describe your younger self as whatever feels right to you, no matter what you think of yourself as now.