Hm. I suppose I was first exposed to mythology through my love of fantasy and sci-fi. As a kid, I was a voracious reader. I grew up on books like The Dark Is Rising sequence, Green Knowe, The Weirdstone of Brisingamen -- and though at the time I didn't understand the mythology behind them, I fell in love with those stories. (I still adore The Dark Is Rising, and the way the movie thoroughly butchered such a great book makes me sad.)
Around grade 5 I discovered Geoffrey McSkimming's Cairo Jim novels, and through the eponymous archaeologist-poet's adventures through antiquity (accompanied, of course, by his faithful companions Doris the talking macaw and Brenda the Wonder Camel) I was introduced to the worlds of ancient Greek, Maya, Norse and Egyptian civilisation, and their gods as well.
(Incidentally, although there are over a dozen Cairo Jim books, I only own one of them. I've had it for years but when I rediscovered it recently, its title made me chuckle. It appears that out of the entire series, the one book I ever bought is Cairo Jim and the Alabastron of Forgotten Gods.)
Around the same time I also got really into Stargate SG-1, and one of the things that really drew me to the show (aside from the wacky space adventures) was the way they incorporated mythology into their stories (tl;dr, the pyramids really were built by UFOs and all the gods ever are evil aliens. Except the Norse ones, who are nice. And the Aztecs, who may be giant glowy things, they never really explained that bit. Look, I don't know, I didn't write it.)
So though I wasn't really exposed to the actual myths and pantheons until high school (studying the Greek gods was the one good thing about year 7 history. Our teacher was a horrible old hag who could make even the most compelling material as boring as batshit), I suppose it was always something for which I'd held a fascination.
Sci-fi and fantasy rekindled my interest in mythology later on -- Neil Gaiman in particular, and especially American Gods and The Sandman, really cemented my love for it and compelled me to start doing some serious reading into ancient myths.
So... tl;dr, a love of sci-fi/fantasy and general geekness. Though I wish I'd had somebody to tell me mythological bedtime stories, that would have been brilliant. xD