Fountain of Youth
My favorite book ever has probably got to be "To a God Unknown" by John Steinbeck.
I actually have a post (the one below this within this forum) that is titled "some favorite fiction..." I list most of the books that have really hit me and that I think have broad appeal. I don't think I would recommend Troilus and Criseyde or Gravity's Rainbow in this forum.
The Wheel of Time series by Robert Jordan are actually in the fantasy genre, not the sci-fi genre if that makes any difference.
When I was growing up my favorite author was Madeline L'Engle. She wrote A Wrinkle in Time, A Wind in the Door, and many others. As an adult, I still like to take an afternoon and re-read them. She has also written some adult books which I've enjoyed, though on a different level than her children's fantasy books. I learned the words pheromone, tessaract, seraph, and others from those books long before I ran into them elsewhere. LOL-that was way back before email so I didn't see 'pheromone' in every other junk mail message because there were no email messages:) During my formative years I also liked Steinbeck a lot, though I hadn't read my favorite book by him- or anyone- To a God Unknown, until I was in my mid twenties.