I didn't always know I was a trans girl, for most of my life i didn't even know what transgender was! However, other kids always said I was too girly for a boy and most of my best friends were girls so it should have been obvious to me.
Anyway, throughout middle and high school I was absolutely miserable and never really knew why. Then during my final years in high school a revolution happened. TV shows like "I am Cait" (yes im guilty of watching a few episodes) and "I am Jazz" began to spring up and I found myself hooked. I couldn't stop watching these shows and wanted to learn more about what it is to be "transgender".
Though, it wasn't until my freshman year of college when I was away from my family that I was able to come to terms with my true identity, and I didn't do it alone. During that school year I was horribly depressed barely able to make it out of bed to go to class or hang out with my friends so I sought out the counseling center at my college and through both individual and group counseling sessions I was able to determine and accept my identity not as Joseph but as Josephine.
So if you're having any doubts about your identity let me tell you: It is never too late to accept yourself.