I always loved movies but only watched children's films, Disney, The Goonies or whatever. I'd go see the new superhero movie or whatever was coming out.
Then around early high school I start wanting to watch more serious movies. Like every 15 year old I got started on Tarantino, Fincher, what have you. I started watching what my favorite directors like and that broadens things up into foreign film territory. I started browsing boards like this and seeing patrician infographics and I was like, I wanna be like that.
It's pretty much been like that ever since. I find out about a director, a style of film, a movement, an important period, and I want to get a taste of it. And if I like it I want to see more.
I think the first real art house film I saw was Eraserhead. I didn't really "like" it at the time, per se, but I was fascinated.
It didn't really incite my interest in art house but it did stick with me. I think that was my first exposure to something totally different and surreal.
Most cinephiles develop that way, I think. It's just a gradual desire to see new things and be more informed. There's definitely a competitive feeling for me. I don't like the feeling of having to tell someone I haven't seen something. And there's still a ton of classic films I've not seen yet and I try desperately to conceal that.