In the fifties we didn't talk much about YA [Young Adult] novels because what we would consider a YA novel today was then being published as a straight
trade novel. The YA genre was just being born. And basically YA novels are novels which have a young protagonist through whose eyes we see the story. Novels of science fiction were still being published by the sci fi presses, and it never occurred to me to send any of my manuscripts to anybody but a trade publisher.
That may have been naive, but I think it was a good choice.
So WRINKLE, when it was finally published in 1962, after two years of rejections, broke several current taboos. The protagonist was female, and one of the unwritten rules of science fiction was that the protagonist should be male. I'm a female. Why would I give all the best ideas to a male?
I have always had difficulty with the concept of categorizing a book according to reading level... What does a ten-year-old think about? What does an 18-year-old think about? Some ten-year-olds think about things 18-year-olds wouldn't dare to dream about. They just don't know how to read the words yet... Perhaps my opinion is colored by the fact that when I was ten years old I was reading "adult nonfiction" and my reading level was assessed at three grades ahead... Interestingly, by the time I was 14, my reading comprehension level was dropping off. That may have been because I was assessed using material that was read to me rather than material in braille; but the truth is that I have continued to find "adult" wording difficult while I can handle the concepts if the words are at a level I can understand.
What does an adult read about? Do adults only read about affairs and murders? That was my impression as a child... But perhaps once in a while an adult might pick up a "young adult" novel or even a "children's book" and find it thought-provoking. Is the book then still a young adult or children's book? Why does it really matter? Have we really left our childhoods so far behind that we can't also identify with that 13-year-old protagonist? I haven't.