Audio books were available when I was in my teens, but to tell the truth I scoffed at them. I was, and am, a fast reader, and I can read in 3 hours a book that in audio format takes 8 hours to listen to.
But audio books have more to offer than just having someone else read a book to you. With the proper narrator, you can be transported into the world of the book, and its almost as good as a radio show. That's what "The theatre of the mind is" - using your imagination to conjure up pictures in your head as evoked by the descriptions in the book, assisted by the voice of the narrator.
So nowadays I listen to audio books in my car whenever I'm on the road, and old time radio shows at night as I'm relaxing for the evening.