My Life as a Teenage Robot - Season 3 - Eps 2: Good Old Sheldon
Turns out, poor Sheldon was stuck on the aliens' ship when Jenny got rid of it (in the previous episode), and he's been spending decades trying to get back to Earth (even though it's only been a short time on Earth since he left). Hopefully, Jenny can get him back to his proper age.
About My Life as a Teenage Robot

Title: My Life as a Teenage Robot
First Air Date: 2003-08-01
Last Air Date: 2009-05-02
Status: Ended
Rating: 7.358/10 (from 166 votes)
Language: EN
Seasons: 4
Total Episodes: 76
Network: Nickelodeon Nicktoons
Genres: Animation, Comedy, Action & Adventure, Sci-Fi & Fantasy, Kids
Production Companies: Frederator Studios, Nickelodeon Animation Studio
Synopsis
Jenny, aka XJ-9, is a super-powered robot with a super-sensitive teenage heart. Her primary function is protecting the planet from disaster, but – like all teenagers – she has her own ideas about how she would like to live her life. Bored with being a superhero, Jenny wants to do something really exciting – like go to high school!
Cast

Janice Kawaye
Jenny (voice)

Candi Milo
Dr. Wakeman (voice)

Chad Doreck
Brad (voice)

Audrey Wasilewski
Tuck (voice)

Quinton Flynn
Sheldon (voice)