Tried reading it in its spot on the AO rotation when my oldest two were that age. I think maybe years 4-6? They both HATED it. My oldest wrote a very persuasive essay one time when I assigned him an essay, arguing that we were spending too much time on heathen beliefs. I finally discontinued it. We did the much lower-key Tanglewood books along with the D’Aulaire book on myths, and we use the Age of Fable as a reference when we encounter an allusion in poetry or literature and want to remind ourselves of the story.
That said, my older two boys wish now that they have taken the National Latin Exam a time or two that they had paid more attention and read more mythology, as there have been mythology questions each time they take the test, and our Latin book does not cover many of them.