In the beginning was the masters mile — exhibition events at indoor meets for middle-age men. David Pain of San Diego organized these races and found them popular enough to start a sport — masters track and field. (Older athletes had run track, but David’s role was being the Johnny Appleseed of age-group athletics.) More than 50 years later, M45 middle-distance star Peter Brady is continuing the Pain legacy. First he helped found the Masters Milers group on Facebook (with 1,000 members). This month he’s launched a podcast — free audio interviews on Apple iTunes. (A related website is a…