I only started thinking I might be trans a few years ago at age 50. But looking back, there were all kinds of signs. When I was 7, my best friend was a girl. Everyone else teased me, so we stopped being friends (major regret, but hey, I was 7). In preschool, I made two friends, both girls. As a teen, most of the people I was interested in being friends with were girls.
I've always been most interested in movies and books about strong female central characters, and always enjoyed listening to music by female singers. All of this started falling into place as I began looking back.