At 12 I was reading wildly random choices from the SF Book Club and hating most of them. I liked space opera almost from the first and I still do. But reading Tolkien, also discovered at age 12, was analogous to the first time I heard a string quartet at age 7: I was overwhelmed by the joyful realization that what I wanted without knowing how to describe it was actually there to be found. I wouldn't have to forever put up with pale, anodyne books or music. Real books, real music was so substantial I wasn't able to entirely encompass it when I first encountered it, which is what you're saying I think. It made us bigger and that felt so good.