What best explains the reason why the author of A Girl Named Zippy tells the year that she was born?

so the reader knows how old she is today
so the reader knows how old she is in the story
to give the reader a sense of when the story takes place
to give the reader a sense of why the story takes place

The best explanation for why the author of "A Girl Named Zippy" tells the year she was born is to give the reader a sense of when the story takes place.