I didn't watch it when it first came out, I was probably 9 or 10 when I finally saw it. Instantly loved it. And I knew why. It wasn't even the first time I'd seen that plotline, when I was 8 I read the Song of the Lioness quartet, which is about a girl who says she's a boy so she can become a knight. And that she was living as a guy, I knew I wanted that so badly. Like Mulan, she ended up going back to living as a girl, and even enjoying life that way. And I felt betrayed when I saw that. I liked to pretend the ending never happened, because I couldn't understand why she'd give that up.
I think that convinced me to tough it out when I hit puberty, because I thought if I waited long enough, I might get used to it like Alanna (the protagonist) did. In a way Mulan was much less personal, practically comedic and she was clearly uncomfortable in a male role at times. But you got to see Alanna hitting puberty and freaking out entirely, just like I did, even though for her it was for mostly different reasons. The most valuable part of Mulan for me was the Reflection song, but lots of things in Alanna hit home.