How old is the narrarator in The Scarlet Ibis?

The narrator in the story is actually Doodle's big brother as and adult telling the story. The story begins using adult language and syntax, but as he slips into telling us about his childhood memories of Doodle he begins to take on a childlike persona and the mood and tone of the story change. The begins to sound very much like a child is telling it about his younger brother at the time things are happening. This is actually a very clever way of writing the story because we get some insights from the adult narrator that we might not have gotten had the story actually been told by the child himself. For example, at several different places in the story Doodle's brother expresses his remorse for the way he treats Doodle, like leaving him in the loft knowing Doodle couldn't climb down the ladder without help. The narrator recalls how he felt at the time and how he felt after having heard Doodle's screams.