Harry didn't receive his letter to Hogwarts when he was eleven, or twelve, or thirteen. In fact Harry was never going to find his Hogwarts letter in the mail, because Hogwarts didn't exist. It was just a story he told himself to cope with the real world he lived in.
Harry Potter is abused boy creates a magical tale that reflects the reality he lives with himself as the hero. After being rescued from his uncle, Harry learns to deal with his new life, friends and worries the only ways he knows.