Futurama Episodes

When Fry and the Planet Express gang realize that at 161 years old, the Professor has become too crotchety to handle, they decide he needs to be “youth-a-sized”. Traveling to an asteroid, they register the Professor at a posh resort where their full-body bath in searing hot tar is guaranteed to turn back the clock. Through a series of unfortunate accidents, the bath covers not only the Professor but also everyone else and all are affected by the treatment. Back at Planet Express, a now 53-year-old Professor tries to keep a now 13-year-old Fry and other kids under control while looking for a way to reverse the effects of the tar treatment. Meanwhile, “the kids” all react to their newfound youth, including Leela, who decides she could have a taste of the childhood she never had as an orphan
wikipedia.org summary:
The crew’s attempts to de-age Professor Farnsworth result in everyone returning to their more youthful stages. While Farnsworth seeks out a way to re-age the crew, the newly-teenaged Leela takes the opportunity to experience the parental childhood she never had.
imdb.com summary:
After an overdose at a health club makes the Planet Express staff get younger and younger, they have to find a mysterious Fountain of Aging. Meanwhile, Leela experiences the teenage life she never had with her parents.