This is a fascinating question to ponder, but oh so difficult to answer.
My impression of gay people was formed at a very young age, and it was a positive impression, so likely that wouldn't change. Transgender and bisexuality...I did not learn about the first until my teenage years, and even then I had a naive and mistaken idea of what it meant. Same for bisexuality, only my understanding of that came years later. Probably up until I began considering transitioning was I ignorant about the GLBT world.
I wonder if my gender had been different in my younger years, would those events and influences that shaped my attitudes towards GLBT people had even occurred? Or would I have differently interpreted them and drawn completely different conclusions?
I think I would have been accepting of the GLBT community, but still unaware of the nuances of truly accepting people in those categories and perhaps a little stand off-ish about those concepts. A sort of "I don't mind what you do, but I'm not interested in it" attitude. Only in my college years or beyond would I likely refine my ideas about the community and approach it in a more educated and mature manner.