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. Some characters may even deliberately do an age change to close the gap with their love interests; this is most commonly done with a child with a Precocious Crush on an adult becoming older.
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. There's occasional overlap with Time-Travel Romance, at least with those cases where the two characters are acquainted even before travelling to different parts of each other's lives. A subtrope of Age-Gap Romance.
- In Dragon Ball Super, Trunks develops a crush on Mai, who looks about his age but was actually turned into a child due to an accidental wish on the Dragon, and is in fact older than his own mother. Nobody seems to have a problem with this (it's implied none of the older characters recognize the de-aged Pilaf Gang). In fact, Future Trunks is also shown to be in a relationship with the Mai of his own timeline (who was likewise de-aged). Fan opinion is divided on whether the idea is cute or Squick.
- In ERASED, 29-year-old Satoru's consciousness is transferred into his 11-year-old self so that he can rescue his classmate Kayo from a grisly murder. Satoru finds himself developing a crush on her, and they have some Puppy Love moments of romantic tension, but the relationship is never explicit.
- Flip Flappers reveals that Papika was an adult around the time Cocona was born, and even helped raise her. Circumstances eventually caused her to be hit with both de-aging into a child's body and a case of Laser-Guided Amnesia after meeting a toddler Cocona in Pure Illusion, so when they met again as preteens, she fell in love with Cocona the old fashioned way.
- Charlotte And Her 5 Disciples: When the ritual that Archmage Charlotte Eleanor uses to return her magic to the world upon her death instead reverts her into a child, she ponders why and concludes that there must have been a lingering regret in her life. She decides the one thing she regretted never experiencing was romantic love and decides to use her new life as Aria Lissen to find it. Unfortunately, while Aria has no shortage of suitors come adolescence, she is still, mentally, a centuries old archmage. This causes her to think of her peers more as squalling infants than romantic prospects. Ironically, she is completely oblivious to the obvious feelings of her old friend and Secret-Keeper, Jeffrey, even as he helps make sure her new life is a comfortable one.
- In Ah! My Goddess, Urd was de-aged to a child in one story arc and befriended a boy who developed a crush on her. When Urd was restored to her normal age, she told the boy that her "younger sister" had moved far away and gave him a kiss on the forehead to make up for her "younger sister" not being able to come back.
- In the Umareru Kachi no Nakatta Jibun ga Anna no Tame ni Dekiru Ikutsuka no Koto manga, Kazuya Mukai somehow winds up being transported back to his elementary school days, and begins pursuing his love interest from sixth grade. Unfortunately, it goes disastrously and quickly turns into more of a murderous obsession than genuine affection.
- 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 Runaways (Rainbow Rowell); 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 Sonic the Hedgehog (Archie Comics), Amy Rose wishes for herself to be older, partly so she can join the older heroes on adventures but also in large part so she can get Sonic's attention.
- 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.
- Severus Snape is very aware of the age gap problem in The Peace Not Promised, after he gets a chance to relive his sixth year at Hogwarts. He can't bring himself to stay away from Lily, but he feels guilty every time he thinks about them having a relationship when she's the right age to have been one of his students.
- Defied in Not the intended use (Zantetsuken Reverse). Kazuya was somehow reborn in the Castlevania universe after his death, in the body of his teenage self. He doesn't like dating because he was the father of several adult children before he died, and every girl in his (apparent) age range is young enough to be his daughter.
- In 13 Going on 30, Jenna is mystically flung into the future from her 13-year old self in the 1980s to her 30-year old self in the mid-2000s. She has some trouble getting used to the change, and her best friend even has to intervene when she starts chatting up a 13-year old boy at a party. Still, the only person she's really comfortable pursuing a relationship with is her now grown-up childhood friend Matt, who is already engaged to someone else.
- 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. When Josh finds the magical wish-granting machine and makes a wish to be a kid again, he invites Susan to become a kid alongside him, but she refuses and brings him home to his parents while disappearing from his life.
- In 17 Again, Mike is aged down 20 years from 37 to 17. When he starts attending high school again in the present day he's a Chick Magnet (due to being played by Zac Efron). He has to deal with an Unwanted Harem of teenage girls including his own daughter, who are attracted to him and don't know his real age. This trope is one sided: he is not interested in any of these girls, instead trying to win over his wife, who now thinks he's a high school student who weirdly resembles her husband and Likes Older Women.
- 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 the Stargate SG-1 episode "Fragile Balance", 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.
- The Legend of Zelda:
- In The Legend of Zelda: Majora's Mask, the young woman in charge of the Treasure Chest Shop in Clock Town is slightly dismissive toward Link when he's in his real form as a Hylian kid. But when he transforms into an adult Zora, she calls him handsome and gives him a discount for the minigame while making coquettish giggles.
- 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.
- In Tales of Symphonia, Genis has a crush on Presea, who is technically in her 20's but physically the same age as him due to a failed experiment stunting her growth for over 10 years.
- In Tomodachi Life, you can de-age a mii using a Kid-o-matic. Once they're a kid, they are able to fall in love with other child miis. The same thing happens in reverse if you use an Age-o-matic.
- 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.
- The situation between Lil' Miss and Hoohoo in Mayo's Youtube series Lil' Miss and Hoohoo is actually this, despite her appearance and mannerisms. This is supported by character information from their Twitter accounts, as well as a post-credits scene at 5:12 in the second episode. The two are happily married.
- Considering what a Super Mushroom can do, it's most likely a similar situation to Mario needing a mushroom to match Peach's height.
- 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 Young", 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 effects wear off and she returns to her proper age with no memory of what happened leaving him to flounder for an explanation.
- Not what actually happened, but in The Smurfs (1981) adaptation of "Romeo And Smurfette", Papa Smurf finds himself in love with Smurfette and wishes that he were 450 years younger.