Although some members will disagree, a popular theory for the crossdressing (and not transsexualism) is that it came about by early sexual imprinting. People will say they are not sexual when they're little and it's true that little kids don't have sex. But one's sexual development does start in the toddler years:
http://kidshealth.org/parent/growth/...elopment.html#
Kids do discover quite early (3-5 years old) that touching themselves feels good for example. And I remember having intense crushes on boys at an early age, in fact I think that my first love was Mighty Mouse! Seriously. I was six years old. I can still remember the feeling when I heard, "Here, I come to save the day!" I would get butterflies in my stomach when I watched the cartoon. (And sadly, for most of my adult life I did believe that men's purpose was to save the day. I think I had a Cinderella syndrome.) :p
You describe some pretty powerful elements that might well have imprinted your eventual desire to crossdress: the intensity of the feeling as you tried on a piece of clothing worn by a girl you especially liked, and the excitement associated with the taboo.
A number of different things could easily imprint a multitude of CDers at an early age.
Not to go on and on, but my SO had an insight about how an insignificant incident when he was little, affected fears that he had as an adult. This has nothing to do with gender, but the principle is the same. Their family was driving in a rough neighborhood in a large city that was predominately black. He heard his father say, "I'm locking the doors". (Sorry for the non-PC story, but this was beyond my SO's control and it happened 50 years ago). Anyway, as a young man he often needed to pass through that neighborhood and he couldn't figure out why he felt nervous, until he remembered where that had come from when he was a child. A 2 second incident when he was 6, informed reactions he had when he was 20. For some reason, the urgency in his father's voice made a strong impression on my SO.
I think we are a conglomerate of our past experiences, even seemingly insignificant ones.