I didn't even realise properly until I was in my early twenties, lol.
I remember meeting a friend of the family when I was around 10. They identified as female, but liked to dress as stereotypically "male/butch." I remember thinking they were so attractive. It didn't even matter to me that they were a woman.
I always had crushes on boys, but I didn't pay that much attention to other girls. I could always see why they were attractive but I didn't know if I saw them much in that way. A guy used to pick on me in school randomly for being "a lesbian", and it made me question myself then. I thought it wouldn't be so bad if I actually was deep down.
I was in a gay bar with my friends, and another woman came over and flirted with me. I wanted to kiss her so badly, haha. It began to sink in that maybe I wasn't totally straight. After thinking about it, I would look at women and feel the same kind of attraction to them. I realised it wouldn't matter what gender or genitals someone has, as long as I liked them. I came across the word pansexual and felt like that's what I'd been trying to pin down.