I had a couple of amazing things happen probably around age 12 (grade 6) that probably tipped me in that direction.
Like most young boys I enjoyed some computer games, and those were the days of DOS games with computed-generated sound effects and ridiculous pixellated graphics. One of the games we would play was "Scorched Earth", a tank fighting game (very educational for physics ;) ) and the computer teacher had customized the taunts and death messages to localize them to our school. I think that was the first moment where I realized that people wrote software, and that if my teacher could modify something like a game, maybe I too, after I was grown up and educated and experience, maybe I too could enter some chat lines in a TXT file and modify a game :P
The second thing that probably changed the course of what I ended up doing was creating a basic HTML page in Netscape Composer. It looked kind of like WordPerfect, but you could change the background colors of the table cells! I was hooked, whatever "HTML" was I knew it was better than WordPerfect because it had colors.
So from then on I learned HTML, and CSS, though I never would have imagined that would be what I do for a job. I thought all through school and even college that I wanted to design, or animation, or something visual like that. I just didn't realize responsive web design hadn't been invented yet :D Now I know what I'm supposed to do!