As a fetishist, my initiation was a little different than most described so far. My first experience in girls panties was around the first or second grade when my mother ran out of clean underwear for me, she had me wear a pair of my sisters to school. I recall a vague awareness of something stirring within, and that I liked it. But, I don't recall any follow up.
Then, when I was in the 5th or 6th grade, a buddy described how much pleasure he got out of rubbing his mother's panties on "himself". [I am trying to avoid getting banned. :-)] So, I tried it. At some point I figured if it felt this good to just rub, what must it feel like to wear. And, later, if panties were this much fun, what about the rest of the lingery ensemble. And the rest is, as they say, history.