Bewitched (1964)

Season 8: Episode 19

Serena returns for the last time and babysits with Tabitha and Adam. Larry comes by to return a golf club and Serena does an Abby Cunningham on him. Larry hurries off, but not before Serena gives him a pill to be young and active (pre-Viagra!). It makes him younger, all right, by ten years! Larry gets even younger and younger and everyone is very worried about him. Serena gives him an antidote which turns him back to normal.