Never Too Old for Children's Literature

A children's story which is
enjoyed only by children is
a bad children's story.
The good ones last.

C.S. Lewis

"Where the children's story is simply the right form for what the author has to say, then of course readers who want to hear that, will read the story or re-read it, at any age. ... I am almost inclined to set it up as a canon that a children's story which is enjoyed only by children is a bad children's story. The good ones last. 

"...the neat sorting-out of books into age-groups, so dear to publishers, has only a very sketchy relation with the habits of any real readers. Those of us who are blamed when old for reading childish books were blamed when children for reading books too old for us. No reader worth his salt trots along in obedience to a time-table."

C.S. Lewis On Three Ways of Writing for Children

"Some such readers, in virtue of
their hearts being young and old
both at once, discern more in the
children's books than the children
themselves."

George MacDonald in 
Ranald Bannerman's Boyhood

"But I find I have been forgetting that those for whom I write are young -- too young to understand this. Let it remain, however, for those older persons who at an odd moment, while waiting for dinner, or before going to bed, may take up a little one's book, and turn over a few of its leaves. Some such readers, in virtue of their hearts being young and old both at once, discern more in the children's books than the children themselves."

George MacDonald in Ranald Bannerman's Boyhood

[NOTE: Please never take the word of any Christian author for ultimate truth, but rather check it against the Bible. MacDonald was a fallible man with some unorthodox/unbiblical beliefs and both he and Lewis were also influenced by the unbiblical evolutionary worldview. That said, their works contain so many gems that draw me closer to the Saviour.]