I'm to scatterbrained to read other responses but anywhoo, here's mine.
It went something like this: It was back in 2005, I was 29 at the time, and I was reading some guy's profile on OKCupid, it said he was trans and I thought "Heh, me too. Wait.. what??"
After that it took about 4 years before I sat in my doc's office and asked for a referral to the gender clinic.
As for being a late bloomer, having that wee epiphany explained a lot. Like how I had been jealous of trans women when I found out they existed as a young teen. I was jealous that they could DO that. Years later I found out there were trans men, and spent a fair amount of time searching for info online, looking at top surgery pics, thinking "If only that were possible here" (For some reason I didn't think that could be done in my neck of the woods, I thought people had to pay up and travel to the States for it.. Color me stoopid) At that point I STILL hadn't realised I was actually trans myself. Until that day in 2005. After that I found more accurate info on the process, but put it out of my head since I had a kid, health issues I thought would get in the way etc etc. Then I decided I'd go for it when he had turned 18. Well I didn't wait quite that long, fortunately. I was already passing and full time when he was 18 last year.
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Ok waiting for a video to buffer so I can add some "when I was a kid"-stuff.
I never had a conscious thought that I was really a boy when I was a kid. Still, there might have been small clues, such as beaming on the inside when a kid said "Hey, you boy" to me, and the disappointment when my friend said "She's a GIRL!!" all offended on my behalf. As for toys and whatnot, I liked boy-stuff and girl-stuff alike. I had this lovely pink slik-like dressI used when I was 9-10. Mind you, it didn't come with the manners and grace a parent would hope for. XD I would roll around in the dirt with toy cars and sew doll clothes by hand. I grew up with two older brothers who were quite the influence on me, and parents who didn't really care what I was up to, as long as I didn't go drown or get myself run over. As a teen I was more about not standing out than anything else, so I was the anonymous grey mouse in the background. I tried being all girly and stuff, like my best friend, but blimey, what a sad effort.

But all in all , I guess I lived a somewhat gender neutral childhood.
I have wondered what it would have been like, if I had been forced to be more girly by my parents. Maybe that would have led me to realise at a younger age.. or maybe I would just have been really miserable without knowing why.