If Romney wins in 2012, he will be reelected in 2016. All presidents who defeated an incumbent have gone on to serve full terms. In 2020, the youngest "50's kids" would be 61--pretty old to be president.
Carter? Benjamin Harrison?
Carter isn't a good example, he was running against Nixon's ghost, not Ford. As for Benjamin Harrison, I am referring to only post-WWII elections.
Here's another relationship that will blow your mind - no President with a "J" in his name has ever served two full terms.
Well, I am only referring to the post-Jacksonian era. Jackson and the five preceding Presidents were all Js, and four of them including Jackson himself served two full terms. But ever since, the letter has been cursed.
And in case you cite William Jefferson Clinton - I'm only referring to first and last names.