Postman Jim Ed Bull

Postman Jim Ed Bull

Tom Moroney/Bloomberg

His sorting finished inside the Mangum, Oklahoma, Post Office, Jim Ed Bull heads out to load his Ford Ranger with the day's mail. Bull is responsible for the longest mail route in the U.S., 187.6 miles (301.8 kilometers) around and through the tiny towns of Duke and Eldorado in drought-stricken southwest Oklahoma. Bull, a retired high school principal at 72, went back to work for the Post Office and is part of the fastest-growing segment of the U.S. labor force -- those who work past their 65th birthdays.