There are few people in the football world that would argue that Peyton Manning retired too early. In fact, it's likely that you wouldn't find a single person who would disagree on that topic.
Peyton Manning retired at the perfect time - at the top of the world, a Super Bowl trophy in hand. The perfect ending to a storybook career of one of the best to ever play the game.
Sure, Manning could have stayed another year and tried to win another with the Denver Broncos with a historic defense, and a stellar receiving duo of Demaryius Thomas and Emmanuel Sanders.