In my early teens, if I recall correctly - the mid 1970s. I was too young for it emotionally at the time and had to let it alone for a bit. It completely blew my mind.
I reread The Lord of the Rings a couple of years later and was hooked by its themes of friendship, loyalty, and self-sacrifice against deceit, treachery and avarice. I've reread the story at least annually since then. It is my Bible.