"The Old Man and the Key" is the thirteenth episode of the thirteenth season of the American animated television series The Simpsons. It first aired in the United States on the Fox network on March 10, 2002. In the episode, Grampa Simpson falls in love with Zelda, a woman who has just moved into the senior home in which Grampa lives. However, Grampa is not the only one in the home who is infatuated with Zelda.

The thirteenth season of the American animated television series The Simpsons originally aired on the Fox network between November 6, 2001, and May 22, 2002, and consists of 22 episodes. The showrunner for the thirteenth production season was Al Jean, who executive-produced 17 episodes. Mike Scully executive-produced the remaining five, which were all hold-overs that were produced for the previous season. The Simpsons is an animated series about an American family, which consists of Homer, Marge, Bart, Lisa, and Maggie. The show is set in the fictional city of Springfield, and lampoons American culture, society, television and many aspects of the human condition. This is also the last full season to use cel animation, though four episodes from this season's production cycle would air during the following season as holdover episodes.