As a young child I fell naturally into the middle of the "typical" range for little girls (which was to later prove inconvenient because my body wasn't female!) and I thought I was a girl and was accepted by (most) girls as one of them. It wasn't until starting school that the problems really started because the more my mother and teachers tried to push me into "being a boy" the more I protested and rebelled. Developmentally, my childhood and adolescence was typical for a girl.
I started living part time as a girl about age 15 and found it remarkably easy to 'pass' as a girl. By 19 and going away to college, I simply couldn't pass as a guy if I tried - within 5 minutes of my best effort, people would be looking at me funny and saying "That's not a guy!" I don't know why or how but I guess enough 'leaked out' to attract suspicion.
I never did understand boys and they always treated me with suspicion, even the ones I had grown up with who knew I was supposed to be one of them. Girls, on the other hand, I understood and was usually accepted much farther into "the inner sanctum" than any other supposed-to-be boy.
With SRS/transition at 24, all I had to do was stop trying, just let my natural self flow, and nobody batted an eyelash.
In all fairness I was diagnosed (by Dr. Benjamin himself) as a "Type VI transsexual" at age 17 with the phrase a "complete psycho-sexual inversion", which mean pretty typical girl in a seemingly male body, the most extreme diagnoses . So, for me, it just meant "stop pretending".