I suspect that it's somewhat innate. My family didn't read -- I don't remember anybody around me reading, yet from early elementary school I remember checking out two books from the library every day, one to read in the hallways when walking to the bus, on the bus, and through the evening, and one to read the next morning on the way back. Yeah, most of it was just "junk", like the Hardy Boys, or choose your own adventure books (where I HAD to read every possible path), but even beyond that I would read everything -- milk cartons, cereal boxes, etc... I read so much that my parents would get on my case and tell me that I needed to live in the real world.
That continued until mid high school, when I got my first computer. My reading slowed down quite a bit as I spent most of that time programming, I loved it (still do, though doing it professionally isn't nearly as fun), so it was a while before I picked up the reading habit again -- starting with my Newton MP100, where I found Project Gutenberg books and started reading those on my device (and those after that), and it really kicked into overdrive again when I bought my K3, where I went back to multiple books per month. There have been periods of more or less, but I've been back at it ever since and really wish that job/chores didn't take so much time, but maybe some day when I retire I can go back to "two books per day" (well, probably less, most of what I read now is a bit more complex). I did manage to convince my wife on our vacation last week to reserve some time to just read -- we're always just go-go-go, and it felt good to just put a folding chair next to a river and read for a few hours.
EDIT: My favorite "teacher" in high school was the school librarian, and my elective class was to work in the library, where I implemented a dBase III database w/ a barcode scanner to track checkouts and to have an online card-catalog, and then they hired me for the summer to work in the school councilors office typing in the entire card catalog, and then putting the little barcode stickers in every book. I have to admit to having entered a Pepsi can or two into the catalog too!
I would spend all of my lunches in the library where my friends would talk about scifi books, and would ditch all of the school pep rallies to hang out in the library, which he allowed me to do even though he wasn't supposed to -- haha -- I got caught once though because I got an award from the business department for being the fastest typist. I didn't expect anything since I was a junior and it was supposed to be for seniors!