St. Petersburg, Florida has this nickname because of the large number of retirees there. (My high school driver's ed teacher once made the remark, "People say the old people live in St. Pete. That's not true -- the old people live in Miami. And their parents come to St. Petersburg!") Even the St. Petersburg Times acknowledged the nickname on March 3, 2004 (while noting that it had been chosen as one of the U.S.'s most livable cities).