Wow! You have been de-aged! Isn't that cool? Now you can do the things younger people do... why does that kid look so attractive?
This trope is when after a Fountain of Youth, or Overnight Age-Up, characters find another character of their newest age attractive and/or falls in love with them or vice-versa. The effects may or not may persist when the character is reversed to their real age.
It often occurs in fanfic, especially Peggy Sue fics, often with The Mind Is a Plaything of the Body invoked to try and handwave away any squick. How successful that is is up to the reader. A subtrope of Age-Gap Romance.
- Runaways has done a few variations on this trope:
- In "Dead-End Kids", a series of circumstances cause the team to be sent back in time to 1907, where Victor falls in love with a local girl, Lillie. It's ultimately revealed that the whole sequence of events was set in motion by Lillie's older self, who remembered Victor as the love of her life and thus hoped that he would be convinced to bring her younger self into the present.
- Inverted in Rainbow Rowell's Runaways; Gert is brought forward two years in time in order to prevent her death at the hands of Geoffrey Wilder. Since her boyfriend Chase was already four years older than her when she died, he's now much too old for her.
- In the "Best Friends Forever" arc, Molly's new friend Abigail is a middle-aged woman who is under a spell that allows her to remain 13 forever. Having grown tired of watching everyone she loves outgrow her, she tries to convince 13-year-old Molly to take the same deal so that they can be together forever. Whether her interest in Molly is platonic or not is not clear.
- In the Green Lantern franchise, Green Lantern Corps member Arisia has herself aged up with the help of her Green Lantern ring so that she would be a suitable romantic partner with her fellow member Hal Jordan, who originally saw her as too young.
- In the Harry Potter fanfiction A Battle of Subtlety and Manipulation, Narcissa Malfoy and Bellatrix Lestrange are automatically divorced from their husbands when each husband was caught in the act of casting "Avada Kedavra" as a Death Eater and thrown in Azkaban. From there, it was revealed that the women born to the Black family have just enough trace amount of Metamorphmagus talent to slow down their aging but Narcissa and Bellatrix had both previously drank a potion that forced them to age at the same rate as everyone else. After taking the antidote to that potion, they regain an appearance of youth akin to Harry Potter for easier shipping with him.
- After Josh from Big ages from a kid to an adult, he begins a relationship with Susan, an executive at the toy company he works for.
- The Dresden Files: After the nearly 300-year-old Captain Luccio has her body swapped with a 25-year-old's, she briefly dates Harry, who is in his thirties. Discussed when she complains that the swap has left her dealing with hormones that she hasn't experienced in centuries.
- In the sixth Artemis Fowl book, a complication during Time Travel changes the two protagonists' ages—one from a young teen to a young adult; one from an adult to a teen—allowing them to realize they have feelings for each other.
- Implied Trope in a Stargate SG-1 episode where Jack O'Neill is apparently de-aged into a teenager overnight, but it turns out to actually be a cloning mishap caused by a rogue alien who kidnapped Jack. The clone is allowed to start a new life on Earth, with the real Jack dropping his doppelganger off in front of his old high school and him getting some interested glances from a group of girls.
- In The Legend of Zelda: Breath of the Wild, the scientist Purah is an old woman in a little girl's body after experimenting with de-aging runes. According to the notes she took as she was growing younger, she developed a crush on her lab assistant while she was a teenager.
- True Villains: Defied when the 88-year-old Evil Sorcerer Bayn finds himself the target of the six-year-old Mia's Puppy Love after he's turned into an eight-year-old and De-Powered. Although he becomes a bit less curmudgeonly as a child, he retains his mental age and firmly rebuffs any sign of infatuation from Mia.
- In Adventure Time, Finn has long nurtured an unrequited crush on Princess Bubblegum, who as a 19-year-old (who happens to be Really 700 Years Old) is too old to be dating a thirteen-year-old. In the episode "Too Old", PB is aged down to Finn's age and their romance temporarily blossoms.
- Archie's Weird Mysteries: When all the town's adults are turned back into teenagers (both physically and mentally), the now sixteen Miss Grundy hits on Archie and Reggie. Both are repulsed by the idea, although Reggie starts to warm up to it whilst the two are slow dancing together, right before the affects wear off and she returns to her proper age with no memory of what happened leaving him to flounder for an explanation.