When I was growing up, if I recall rightly, there were just two types of books: Children and Adult and we seemed to do really well with that.
Yeah, I grew up with that too. I think "The Outsiders" was the first book I read that was aimed at teenagers - today's YA. It came out way before I was in that age group - but was still quite popular when I was about 15.
After the children's books, we just went on to reading adult lit. Didn't understand all of it - I was reading Updike, Cheever, Mitford, etc and not grasping all the sociological/psychological aspects - but that's what was available.
I wonder if NA would have been a helpful transition between those groups?
And I agree with lunasspecto - interesting development among today's generations - I have friends who are struggling with their NA children and how to help them move onto "full" adulthood. But other friends have children who've moved through the traditional channels - high school, college, live independently - successfully, so it's not a universal phenomenon.