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* In ''Literature/AcidRow'', Sophie Morrison is in her late twenties, but looks much younger due to her short stature, baby face and tendency to wear her hair in a long plait (similar to how some schoolgirls wear their hair). This leads to some people underestimating her or not taking her seriously, when she's actually quite sharp and fierce-tempered. Unfortunately, it also in-directly contributes to the riot at the centre of the plot; someone sees Sophie going into a sex offender's house and mistakes her as a young girl, leading to rumours that a missing 10-year-old girl is in the house and resulting in the rioters turning up on the doorstep.
* ''Literature/TheAgeOfTheFive'': Most of the Wilds, the White, and the Voices are a lot older than they look. Juran, the leader of the White, is actually over 100 years old, his aging having been stopped by the Circle of Gods when he was chosen to be one of their human representatives. They [[Really700YearsOld only get older]] from there.
* In ''Literature/TheAliceNetwork'', Eve looks seventeen but is actually twenty-two, which helps her [[ObfuscatingStupidity pretend to be young]] and [[TheirFirstTime inexperienced]].
* In the ''Literature/AllianceUnion'' novels by Creator/CJCherryh, FTL travels slows down physical aging by around 25%. So spacer teenagers look like middle school kids, twenty-somethings look like teenagers, etc.
* ''Literature/ArifuretaFromCommonplaceToWorldsStrongest'': Yue, Tio, and Aiko resemble young children. They're actually 300, 500, and 25 years old, respectively.
* ''Literature/AscendanceOfABookworm''
** Myne starts out at age five but only looks three. Her physique is small and weak due to her poor health, which always leaves her looking younger than she actually is.
** Gil, who grew up in a OrphanageOfFear in which dying of starvation was a thing, is sometimes mistaken for being the same age as Lutz, who is actually three years younger than him.
** It's extremely easy to forget that Justus is in his early thirties when the reader first meets him. In addition to being visibly shorter than characters who are still in their twenties, he frequently acts more immature than most of them. Another contributing factor is that as a MasterOfDisguise who sometimes uses DisguisedInDrag, he remains clean-shaven under his real apperance, which is mentioned to be naturally on the androgynous side of male body types. The fact that he serves a character who is both known to be in his early twenties and the one who acts the most mature in many of their scenes together doesn't help matters.
* Firo from ''Literature/{{Baccano}}'' is regularly assumed to be about three or four years younger than he actually is (eighteen and a half). Of course, now that he's taken the [[ImmortalityInducer Elixir of Life]], that disparity [[Really700YearsOld is only going to get bigger over time]].
* ''Literature/BadMermaids'' has the 4,008-year-old witch Maritza Mist, who smeared her tail with immortality paste when she was seven and has looked like that age ever since.
* ''Literature/BeingAbleToEditSkillsInAnotherWorldIGainedOpWaifus'': Cecil looks like a child. She's actually around 14-15, which makes her an adult in the series setting.
* In the Literature/{{Belgariad}} Belgarath looks 70. He's 7000. Proportionally beaten by his daughter Polgara, who looks 30, and is about 5000.
* ''Literature/BludgeoningAngelDokuroChan'' primarily parodies the trope. Dokuro-chan was sent by God to kill Sakura (or make his [[FateWorseThanDeath life worse than Hell itself]]) for the crime of giving humanity immortality. Why? The catch is that all women stop aging at 12, making it a pedophile paradise.
* ''Literature/ACertainMagicalIndex'':
** Komoe-sensei looks very young (no older than ten) and wears bunny pajamas to bed. Yet she is an adult, and her apartment is littered with beer cans and cigarettes. Quite a contrast there. For the longest time, there was no explanation for this, but in later volumes rumors eventually surface that she was the subject of some kind of age-regression experiment (though whenever anyone mentions this in front of her, she denies it).
** In the Natural Selector Arc, there's Oumi Shuri, a Kouga Kunochi who is over 30 years old, but at some time in her life, came upon a disease, probably the Clostridium botulinum bacteria, that stopped her from growing, and maintained her skin and preserved her childish face, and then she had her body modified to the point that she looks around 10 years old.
* ''Literature/TheChangeRoom'': Eliza is forty two, though her husband Andrew thinks she looks twenty still, and is very admiring of her for it.
* In ''The Book of Three,'' the first installment of ''Literature/TheChroniclesOfPrydain'', Eilonwy invokes the trope when talking about the evil Queen Achren, who claims to be the girl's aunt. Achren is described in the narrative as being very beautiful, but Eilonwy assures Taran that "she's older than she looks."
* The title character in Creator/ArthurMachen's short story, "The Bright Boy", looks to be about 7 to 10 years old, but is actually [[spoiler:a man in his 60s]]. The ending reveals that [[spoiler:he was likely conceived by a mortal man and an [[TheFairFolk infernal]] woman.]] It also reveals that [[spoiler:he is a fugitive rapist who is passing himself off as the son of a wealthy couple. Because of his abnormal nature, he stands out like a sore thumb and there is no other way for him to hide from authorities.]]
* ''Literature/CasteelSeries'': Jillian Tatterton, who is 60 years old when her granddaughter Heaven enters her life (much to her chagrin) but doesn't look much older than her 30s. Somewhat deconstructed as Jillian is unhealthily obsessed with keeping her youth, to the point of ignoring any sort of inconvenience in her life so as to not get stressed. [[spoiler:Subverted when she has her FreakOut after being forced to admit that she knew that her daughter was being raped buy her husband, which ages her greatly]].
* In Creator/TeresaEdgerton's second ''Literature/{{Celydonn}}'' trilogy, Gwenlliant is initially 12 years old (in ''Literature/TheCastleOfTheSilverWheel''), and looks it, but thanks to TimeTravel is at least a year older than her official age by the time she is technically fifteen (in ''Literature/TheMoonAndTheThorn'').
* The ''Literature/ChakonaSpace'' setting features the contributor series, ''Tales of the Folly''. While Neal Foster falls into the ReallySevenHundredYearsOld category, many of his friends and colonists and all 12 of his Rakshani Marines fall neatly into this trope.
* Enrei Islio, 21 in ''Literature/ChaosFighters II-Chemical Siege'' is called an ''8''-year-old man due to this trope.
* In the ''Literature/ChaosGods'' series, Ki is 15 years old, but looks eleven; she stopped aging after absorbing a demon at that age.
* In ''Literature/TheChroniclesOfNarnia'', the four Pevensies look like children, and are as far as anyone in their own world is aware, but they are in a sense technically adults because they spent fifteen years in Narnia. Although they did de-age once they went back in England, they are the only people who have gone to Narnia and grown up. This idea is more played with in the fan-fiction universe.
* In the ''Literature/CiaphasCain'' novel ''Cain's Last Stand'', Cain is a nearly 100-year-old retiree who appears to be in his early fifties or so thanks to [[AppliedPhlebotinum regular juvenat treatments.]] Characters who have been receiving the treatments longer can cross into Really700YearsOld, such as Alizabeth Bequin in the Eisenhorn series, who's 170 or so but doesn't look any older than her 20s.
* In Creator/JimButcher's ''Literature/CodexAlera'' series, [[MakingASplash watercrafters]] have an innate healing ability which causes them to retain their youthful appearances even as they age -- Gaius Sextus, for examples, is over 80 but looks around 40. A scene in the fourth book has a cop mistaking the 50-year-old Isana for a streetwalker, until she lifts her hood so he can see her graying hair.
** Mention should also go to main character Tavi. In the first book, Amara guesses he's twelve or thirteen, only to be informed that he's fifteen. [[spoiler:Thing is, Isana's been lying to him about his age: he's actually ''almost eighteen'', since he was born the night Septimus was killed. Granted, his apparent youth is due to her magically stunting his growth.]]
* ''Literature/CradleSeries'': Once a [[SupernaturalMartialArts sacred artist]] reaches Underlord level, their aging slows significantly. It slows further at Overlord, and [[TheAgeless every known Archlord and Monarch is explicitly immortal]] (though most named Archlords are exceptional even by Archlord standards, so it might not be inherent to the stage of advancement). Some of the most powerful entities in the world [[ReallySevenHundredYearsOld choose to appear as children or young adults]]. Furthermore, sacred artists have extremely healthy bodies by default, so even the weakest tend to be fit and spry even in their eighties.
* Santo and Traken from the ''Literature/CurseOfTheBloodFox'' trilogy may look like young people, but they are in fact much, much older than that...
* This trope is in full force in ''Literature/DeucalionChronicles'' -- to the point where it's easier to name characters that actually look their age. Almost everyone stops aging after a certain point, thanks to either natural magic or the alchemical solution Ambrosia. Some Outsiders barely age past puberty. The only exceptions are certain religious groups that refuse Ambrosia and non-CU worlds where it is unavailable.
* In the ''Literature/{{Discworld}}'' novel ''Literature/{{Mort}}'', Ysabell is 16, but has been 16 for 50 years, since she lives in Death's Domain, where time does not pass. We later find [[spoiler:Albert]] is Really700YearsOld for the same reason.
* ''Literature/DocSidhe'': As a pureblood sidhe, Doc ages very slowly. Harrison's initial estimate of Doc's age is off by several decades.
* [[MagicKnight Serroi]] from Creator/JoClayton's ''[[Literature/TheDuelOfSorceryTrilogy Duel of Sorcery]]'' and ''Dancer'' trilogies is [[LittleMissBadass tiny and baby-faced]] enough to pass herself off as a preadolescent in the first trilogy. She's twenty-seven in ''Moongather'', thirty or thereabouts by ''Changer's Moon''.
* In Frank Herbert's ''Literature/{{Dune}}'', the Padishah Emperor, Shaddam IV is said, by Princess Irulan in her writings, to have been in his seventies, yet only appeared to be about thirty five years in age. This was, of course due to the life extending spice Melange. A revised version of this aspect of Shaddam does make it into film adaptations even though he is consistently depicted by older actors. However, he is usually said to have lived for over two hundred years, as in the case of the David Lynch adaptation.
* In P.N. Elrod's vampire novels, vampires who are older than about 20 revert to that age when they die and return. This was most evident with [[spoiler:the once-elderly Gaylen]] in ''Lifeblood'', and is a frequent annoyance to Jack Fleming, who's chronologically in his late 30s yet is regularly called "kid" by people who don't know this. [[spoiler:It also means Jack may never be able to see his parents again, as he doesn't want to tell them he was murdered and his newfound youthfulness would demand an explanation.]]
* Joe the Leprechaun, right before he starts working at Literature/TheEnchantmentEmporium, is said to look like he's barely older than Allie, who's getting an advanced college degree[[note]]One that involves being a research assistant, anyway[[/note]], which would make him no more than 30-35. Thing is, he's a [[ChangelingTale changeling]], 'his' human died, and Joe has no reason to believe it wasn't from old age.... (Keep in mind, if the human was killed a lot sooner, Joe would have spent '''decades''' trying to avoid the 'call home'. The conversation, besides bringing up the 'old age' thing, implies he's been taking his anchoring potion for only a short time.)
* ''Literature/TheEnchantedFiles'': In ''Diary of a Mad Brownie'' / ''Cursed'', when Ms. Kincaid asks Alex how old the girl thinks she is, Alex guesses she's thirty. Ms. Kincaid then reveals she's actually sixty-five, and that the women in their family have ''always'' aged slower than normal.
* ''Literature/ExHeroes'': Multiple characters comment that Billie Carter looks like a teenager, both during the ZombieApocalypse and three years later. However, she'd already been serving in the Marines (where the minimum enlistment age is 17) for at least eighteen months before then.
* ''Literature/TheFamiliarOfZero'': Saito Hiraga looks no more than 13, but is in fact a 17-year-old. Even worse is his {{Tsundere}} mistress, Louise, who only looks ten at the most and is the same age as Saito.
* Several of the secondary adult ''Literature/HarryPotter'' characters qualify here, in particular Dumbledore and Griselda Marchbanks, each of whom are well over 100 years old; it's implied that wizards have a somewhat [[WizardsLiveLonger longer natural lifespan than muggles]]. Voldemort has also ceased aging altogether, being 71 years old by the last book, though his monstrous appearance hardly seems like a fair trade for smooth clear skin.
* Done in ''Literature/HaruhiSuzumiya'' with Mikuru Asahina, who is described in the series as "Lolita-looking". She's seventeen, while the rest of the cast is sixteen. She also happens to be MsFanservice and have big boobs, yet ''still'' manages this title. Then there's the whole [[spoiler:TimeTravel thing]] (and her playful refusal to answer any of Kyon's inquiries about the matter), which makes her real age pretty much impossible to determine. Given the possibilities of future medicine, she could be in her thirties for all we know.
* Creator/RobertAHeinlein:
** Heinlein's stories about members of the Howard Families. These individuals appear to age at a normal speed until maturity, then slow down drastically (easily passing for forty when in their seventies, for example). After rejuvenation therapy is developed, someone who looks eighteen can easily be twenty times that age or more.
** In ''Literature/TheMoonIsAHarshMistress'', Lunar colonists age more slowly due to the lower gravity. In fact, after a hundred years, no one born on the Moon has yet to die of old age, so they don't even know their own life expectancy. When an Earth reporter guesses Manny's age as twenty-two, he thanks her for the compliment and states that he's been married longer than that. Manny's appearance and Loonies' slow aging aren't mentioned until the middle of the book, so the fact that Manny looks so young is a surprising reveal.
* ''Literature/HighSchoolDXD'':
** Koneko is fifteen and looks like, at most, twelve. [[spoiler:This is due to an imbalance in her powers and her rejection of her voluptuous older sister.]]
** Venelana Gremory, Rias's mother, appears to be the same age as her daughter, and younger than her son Sirzechs. Sirzechs fought and established himself in the Three Powers war, which went into a cease-fire in the early 1600s.
* Early in the first installment of ''Franchise/TheHitchhikersGuideToTheGalaxy'', it's revealed that Zaphod Beeblebrox is about 200 years old, which means also that Ford Prefect is as well, since they were childhood friends. It's only mentioned in passing, though, and doesn't really matter much to the plot.
* Gets a passing mention in David Weber's ''Literature/HonorHarrington'' series, where recipients of prolong treatment have a very extended physical adolescence. A visitor from a planet that doesn't have it is disturbed at seeing a combat warship full of what looks like teenagers and even pre-teens. It's also mentioned in passing that sex among crew members is something that happens fairly regularly, so... In the first book the titular character is over 40 and appears to be in her twenties.
** Even newborn babies are OlderThanTheyLook: for a mother who's had prolong treatment, pregnancy lasts eleven and a half months.
** Later Weber tries to RetCon this to rein in the {{Squick}} by mentioning that most of the prolong recipients also have aging treatments in their adolescence, so that their physical aging would roughly match the traditional pattern.
** This also manifests in the older age, as the physical aging radically slows after a certain threshold, so a human in their 120es would look anything from their mid-to-late twenties (Honor's mother Allison, for example) to early forties ([[spoiler:Honor's husband]] Hamish Alexander), depending on the technology's version, and would remain so until their death, which would (projectably, no one with prolong has lived so long yet) come at ~300-350 years.
** The trope also occurs in Weber's ''Literature/EmpireFromTheAshes'', as a combination of biological enhancement, suspended animation, and (among the bad guys) outright {{body surf}}ing.
* Aur, the VillainProtagonist of ''Literature/HowToBuildADungeonBookOfTheDemonKing'', was an old man at the end of his lifespan by the time he finished his mana potion -- rejuvenating himself was the first thing Aur did with his new immense power. There’s also the many demons and other races seen in the series.
* Ceasar Flickerman has been hosting ''Literature/TheHungerGames'' interviews for over 40 years, but doesn't look much older than when he started because of extensive plastic surgery, a very common practice in the Capitol.
* ''Literature/IfHerFlagBreaks'': School elder Tsumugi Ryuukishibara looks like a young child, complete with bonnet; in truth, she was once a fully-grown woman, but shrank to her current height as she got older. No-one knows how, and Tsumugi herself seems to think it's perfectly natural. Rumor has it she's been around since the school's founding.
* It's unknown how old Angela Baker exactly is in ''Literature/InCryptid'', other than much older than she looks. Cuckoos (a.k.a. Jhorlac) can apparently live for several centuries, their longevity combined with their usual total amorality and MindControl powers make them NightmareFuel incarnate. The exceptions to the cuckoo AlwaysChaoticEvil are exactly two, Angela Baker and Sarah Zellaby; both are adoptive relations to the Price family. Alice Price-Healy, the paternal grandmother of the current generation of Prices, is merely OlderThanSheLooks, but she spends so much time in dimensions where time flows differently that if she continues this, she will ''become'' this trope with simple advancing chronological age: The oldest she's ever been was in her mid-thirties, she currently appears to be in her early twenties, young enough to pass as Verity's sister.
* The vampiress Claudia in ''Literature/InterviewWithTheVampire'', the first book of Anne Rice's series Literature/TheVampireChronicles, is [[NotGrowingUpSucks forever stuck in the body of a 6-year-old girl]]. She would've grown into being Really700YearsOld, but was killed just a few decades after she was turned. In the 1994 film adaption of the book, her age was changed to twelve. Considering that Anne Rice wrote the screenplay for the movie, we can assume she changed it to reduce the {{Squick}} factor of the love story, along with pragmatic reasons concerning child labor laws and acting ability.
* ''Literature/InTheMidstOfWinter'': Evelyn, partly due to being very small (at sixteen, she could fit into preteen clothes). Richard sees her getting out of the car he rear-ended, and assumes she is too young to drive.
* ''Literature/JourneyToChaos'': Mentally, Eric is a man in his twenties but his journey through the veins of Noitearc deaged him so he looks closer to fifteen.
* ''Literature/TheKindnessOfDevils'' has Hardestadt Delac and Grete Ravenhallow, both of whom look like they're in their 20s despite being [[spoiler:hundreds of years old. Delac, in particular, is ''thousands'' of years old]].
* Creator/StephenKing:
** In ''Literature/TheStand'', Tom Cullen is said to be looking no more than twenty-three; actually he's at least forty-five. The fact that he acts like a kid probably doesn't help.
** In ''Literature/TheDarkTower'', Roland Deschain appears fifty-something, but is actually hundreds of years old due to Mid-World's [[TimeyWimeyBall wibbly-wobbly timey-wimey]] time/space dynamics.
* The Demons in ''Literature/KyoKaraMaoh'' age at a slower rate than humans, and live longer as well making them this. A good example is the main hero's accidental fiance Wolfrem, who is physically a 16-year-old, but is chronologically 82.
* From the ''Literature/LeftBehind'' books: once the Millennium starts in ''Kingdom Come'', all the naturals who enter this time period experience decreased aging similar to the first several generations of mankind in the book of Genesis, with the children becoming young adults by the time they reach 100. It's not explained how those who were already adults, including those who were already at advanced age, experience this decreased aging at the same rate as the children who enter the Millennium. By the end of the Millennium, however, the longest-living naturals (who at that point are all believers in Christ) end up really showing their age.
* ''Literature/LegacyOfTheAldenata'': All rejuvenated personnel qualify for this, appearing to be in their early twenties or younger, while dating back, in some cases, to before UsefulNotes/WorldWarII. It's occasionally an issue until people start assuming that anybody who looks 20 is probably older. Often a lot older. And you get generation bending, Michael O'Neal Sr's second wife is almost assuredly younger than his son (her age isn't stated, but comparing the children's ages leads to this conclusion).
* Mary in ''Literature/TheLettersFromNicodemus'' looks just like she did when her Son was born (thirty years prior).
* In Creator/GarthNix's ''Literature/{{Lirael}}'', the 19-year-old title character senses her travelling companion Sam [[spoiler:(who turns out to be her [[SurpriseIncest nephew]]...)]] developing a romantic interest in her, so she tells him she's thirty-five with a marvelous skin-care regimen. Her NonhumanSidekick, the Disreputable Dog, backs her up because [[ItAmusedMe she thinks it's hilarious]].
* Although he still looks pretty old, Jack Holloway in H. Beam Piper's ''Literature/LittleFuzzy'' novels is technically 10 years older than he appears physically due to the time dilation effects of hyperspace.
* In the ''Literature/LockwoodAndCo'' series, if the whispering skull's statement at the end of ''The Creeping Shadow'' is to be believed, then [[spoiler:Penelope Fittes is the same person as her supposed grandmother, Marissa Fittes, but doesn't look a day older than the skull first met her, around forty years before.]]
** In the next book it is revealed that [[spoiler:Marrisa preformed GrandTheftMe on her granddaughter Penelope the moment Marrisa died. The skull could only see peoples life energy, not their physical bodies, which is why he didn't realised that Marissa's appearance had changed since he met her.]]
* Akatsuki of ''Literature/LogHorizon'' looks like a middle schooler but is actually in college.
* John Geary, the protagonist of Jack Campbell's ''Literature/TheLostFleet'' series, was a HumanPopsicle in a lost escape pod for over a century. After his rescue and revival, his "posthumous" promotion to Captain gives him seniority over every other Captain in the fleet -- which he exploits to pull their collective chestnuts out of the fire, whether they like it or not.
* ''Literature/LoyalEnemies'':
** [[FirstPersonSmartass Shelena]] casually mentions being at least twice as old as she looks, which is somewhere in her thirties. Justified as she is a werewolf.
** Mages in this book can, through the help of magic, live up to two hundred years but look much younger than that. Shelena does the maths and comes to the conclusion that battle mage Veres is probably about the same age as her if not older, but also looks about the same age as she does.
* ''Literature/TheMachineriesOfEmpire'': Most people in the Hexarchate GalacticSuperpower choose youth-preserving treatments alongside the LongevityTreatment that lets them live past a century, even among the conservative Kel faction, which otherwise frowns on body modifications.
* In the ''Literature/MillenniumSeries'', lead character Lisbeth Salander is mentioned as looking "barely legal", which in Sweden is 15. She's actually 24 at the time of the first book but is described as an "uncommonly thin and fine-boned" person.
* Little My of ''Literature/TheMoomins'' is a tiny girl who looks like a very young child. However, Moominpappa met her before her met Moominmamma, which means that she's older that Snufkin and Moomintroll. Some adaptations give her an AgeLift and make her an actual child, however.
* Magnus Bane of ''Literature/TheMortalInstruments'' is [[Really700YearsOld somewhere upwards of 400]] but is described as looking approximately nineteen.
* Utage of ''Literature/MyMentalChoicesAre'' looks like a little girl. She's 29.
* Rhonda from ''Literature/TheMysteriousBenedictSociety'' is a young woman who can pass for a 10- to 12-year-old just by wearing a puffy dress and wearing a green wig. Her disguise was meant to draw attention away from her age however she still seems young looking.
* ''Literature/TheNeverendingStory'': Time in Fantastica works in strange ways:
** When Bastian arrives at the Ivory Tower, he finds out that the Childlike Empress has not been there "for a long, long time" -- even though Atreyu has not aged noticeably since he met her up there.
** Later, when Bastian makes his way to Dame Eyola's House of Change, she tells him his travels began 100 years ago. Bastian doesn't believe it at first, but he eventually acknowledges it has indeed been 100 years without him (or anyone in Fantastica) aging.
* ''Literature/NicholasNickleby'': The Crummles' daughter is a young adult but looks like a little girl and is claimed to be 10. This turns out to be deliberate as her parents deliberately stunted her growth with gin so that she could continue to pose as a child in their stage act.
* ''Literature/AnObservationLogOfMyFianceeWhoCallsHerselfAVillainess'':
** Shaun is a secondary student, but his petite body makes him appear younger than he actually is.
** In human form, [[spoiler:Pi resembles a small child]], despite being likely older than Cecil.
* Fairly ubiquitous in the ''Literature/OldMansWar'' series. As the title implies, the rank and file of the Colonial Defense Force are recruited at age 75 and then [[BrainUploading transferred]] to new, genetically enhanced bodies that appear to be in their twenties. Those that survive to retirement are given a non-enhanced clone body that is also somewhere in its twenties, for a double dose of this trope. In ''The Last Colony'', John Perry's adopted daughter Zoe affectionately calls him "90-year-old dad" even though he looks about mid-thirties by that point.
* Non-Humans in ''Literature/AnOutcastInAnotherWorld'' age more slowly the longer they live. Orn’tol has the appearance of a 15-year-old, but his actual age is 34. Elven adults can be centuries old.
* In the ''Literature/ParadoxTrilogy'', symbionts stop aging after undergoing the process that turns them into {{Super Soldier}}s. Some symbionts are therefore much older than they look.
* In ''Literature/PercyJacksonAndTheOlympians'', Nico di Angelo looks twelve. He's actually seventy-something from being put in the Lotus Casino, which slows down time. A lot. His sister is also the same. Being set in a world where Myth/GreekMythology is true, many of the other characters are [[Really700YearsOld at least 2000 years old]]. Grover, on the other hand, is thirty-two but looks sixteen (satyrs age slower than humans).
* In ''Literature/ThePictureOfDorianGray'', the character of the title transfers the effects of age and wickedness to a portrait of himself. After twenty years, he hasn't appeared to age a day.
* In the ''Literature/{{Raffles}}'' stories, the titular protagonist becomes PrematurelyGreyHaired during a TimeSkip, thanks to a life of stress and illness.
* In the ''Literature/RedMarsTrilogy'' it's stated that repeated frequent use of the longevity treatment can lead to this. One character is described as looking like she's in her twenties but is really in her nineties. The main characters tend to avert this since they typically only take the treatment once every few decades or so.
* Aletta from ''Literature/RestaurantToAnotherWorld'' looks around 18 but is actually 50, that seems to be normal among demons. Elves and half-elves are between this and Really700YearsOld depending on their age.
* ''Literature/TheReynardCycle'': Pierrot, Nobel's fool is this. When Isengrim refers to him as a young man, Persephone corrects him, letting him know that he is old enough to have been entertaining Nobel (who is at least in his 20s at the start of the series) since ''childhood''.
* In Peter Watts's ''Literature/RiftersTrilogy'' a pedophilic character is captured by a police sting operation which used a man who had been artificially transformed into an apparent child as bait.
* Laura from ''Literature/{{Sarny}}'' is middle aged when she meets Sarny however Sarny mistakes her for someone in her twenties or early thirties. When she dies a few years later Sarny is surprised to find she is a good thirty years older than she had thought.
* ''Literature/TheSecretsOfDrearcliffGrangeSchool'':
** Dr Swan has been headmistress of Drearcliff since it opened over forty years earlier; to look at her, you might think ''she's'' about 40 years old. Then there's the fact that she looks the same about-forty in a photograph dating from the year the school opened. In the DistantFinale, she has been headmistress for over sixty years and still looks about-forty.
** Dora Paule is a student in the Sixth Form. She's been in the Sixth Form for over twenty years.
* Dame Okra Carmine in ''{{Literature/Seraphina}}'' gives her age as one hundred and twenty, but to Seraphina she looks middle-aged or a bit elderly, certainly not centenarian.
* ''Literature/TheSharingKnife'':
** [[WizardsLiveLonger Lakewalkers]] tend to be this to some degree. When Fawn Bluefield brings her [[RescueRomance rescuer/beau]] Dag Redwing home to her parents her father starts an interrogation about his intentions with a question about his age (everyone, including 18-year-old Fawn herself, takes him to be [[MayDecemberRomance somewhere in his thirties]]) over the dinner table. When Dag answers (with some hesitation) "fifty-five", Fawn promptly chokes on her cider.
--->'''Fawn:''' ''(whispering)'' Pa... is 53!
** Also Fawn herself. Her entire family is short, and she is best described as petite. She is constantly mistaken for a child and twice the mistake is only realized by seeing or touching her breasts. The misunderstandings increase when she is standing next to the [[OneHeadTaller two heads taller]] Dag.
* The original ''Literature/ShounenHollywood'' light novel and stage play had "Hiiragi Tsuyoto", who looked so young at his 37 years of age that he was able to pass off as a 17-year-old boy.
* All the main characters in ''Literature/SixWakes'' ([[spoiler:except Paul]]), via cloning and BrainUploading.
* ''Literature/SkulduggeryPleasant''. For example, Tanith Low is eighty, and looks about twenty two.
* In the short story ''[[http://www.benjaminrosenbaum.com/stories/start.the.clock.html Start the Clock]]'' by Benjamin Rosenbaum, a virus that caused humans to stop physically ageing struck the Earth around thirty years ago, making the protagonist, physically 9 years old, technically thirty-nine. An interesting facet of this is that characters who are physically children tend to act like children who have had around thirty years extra experience at being them. Then later in the story, the protagonist meets a girl who is mentally the same age as she is physically, having been infected by the virus at the age of two and only just recently been administered a "cure" to allow her to age naturally.
* ''Literature/{{Slayers}}'':
** The AffablyEvil priest Rezo is the [[ReallySevenHundredYearsOld century-old]] great-grandfather of one of the protagonists, Zelgadis; aside from the two barely noticeable boney lines under his eyes, he looks to be more in his late forties or early fifties. Lina lampshades this when he appears in the first {{Light Novel|s}}, describing him as looking "both young and old at the same time."
** A non-human example would be Hellmaster Fibrizo, who is both the oldest and strongest of the world's five Demonic Lords. He disguises himself in the form of an [[ViewerGenderConfusion androgynous]] young boy in order to decieve people.
* ''Franchise/StarTrek''
** In the ''Series/StarTrekDeepSpaceNine'' [[Literature/StarTrekDeepSpaceNineRelaunch relaunch novels]] the character of Elias Vaughn is introduced. Already [[CoolOldGuy 102 years old]] when introduced, Vaughn appears to be in his late 60s or early 70s.[[note]]This was a deliberate choice on the part of the relaunch authors to show that humans routinely lived significantly longer by the 24th century and aged at a slower rate.[[/note]]
* Any Creator/DanielleSteel character over 40 is said, ad nauseam, to look much younger than he/she is.
* ''Literature/StrikeTheBlood'': Natsuki looks like a grade schooler despite being 26.
* The Eloi, the above-ground people in ''Literature/TheTimeMachine'', resemble [[AmbiguousGender androgynous]] 5- or 6-year-old kids, both physically and mentally. They look five and act five, even as adults. Chapter 4 implies that they stop maturing early, before SecondarySexualCharacteristics have much of a chance to develop.
* Hangbelly in ''Literature/TailchasersSong'' asks Tailchaser if he's six Eyes (months) old yet. Tailchaser awkwardly replies that he's almost nine Eyes old. He's a scrawny cat.
* ''Literature/TalesOfThePack'': Lexie is eighteen, though she looks much younger as a result of her small bust (which [[ACupAngst she dislikes]]), girlish hairstyle, thin build and [[YouthfulFreckles freckled face]]. She isn't happy with this.
* ''Literature/TatuAndPatu'': Due to their small size and odd personality, Tatu and Patu have been mistaken for small children many times, especially in the early books, where they even attend kindergarten. However, other books make it clear that they're just short, weird adults.
* Maria claims to be an adult in ''Literature/TheTestamentOfSisterNewDevil'', and produces a [[MinorWithFakeID fake ID]] to show to cops in case she gets stopped on the street during school hours. However, Basara wonders how effective it'll be, as she looks younger than him.
* The protagonist (and [[UnreliableNarrator questionably sane narrator]]) of ''Literature/TheTinDrum'', Oskar Matzerath, throws himself down the stairs at age three to stop growing. Over the years he exploits his young appearance to get (and get away with) whatever he wants, at the expense of those around him. [[spoiler:He forces himself to start growing again when he's in his twenties, after his father dies.]]
* ''Literature/ThatTimeIGotReincarnatedAsASlime'':
** Rigurd was old enough to be a frail, old man, but after being named by Rimuru becomes a huge mass of muscle who looks to be in his 30s.
** Shizu is in her 70s based on her having been a child during World War II, but she looks 17. [[spoiler:When she dies, her hair whitens and her skin wrinkles to reflect her true age.]]
** Rimuru is both this and YoungerThanTheyLook: in his human form, he looks about 16/17 at the very oldest, but his mental age is around 40, having died as a human at 37 at the start of the series, and being reincarnated with all of his memories. His physical body is only about 3 years old at the end of the series.
** Most demons look like they're in their 20s or early 30s but have [[ReallySevenHundredYearsOld lived over a hundred years]].
* Longevity (alongside {{immortality}}) is a recurring theme in Creator/JRRTolkien's work, resulting in several instances of this trope in ''Literature/TheLordOfTheRings'':
** Humans of Númenórean lineage, such as Aragorn, physically age slower and live longer than normal men. Aragorn, for instance, turned 88 the day he met Gandalf the White in Fangorn Forest. A DeletedScene in the film of ''[[Film/TheLordOfTheRingsTheTwoTowers The Two Towers]]'' has Aragorn reveal his true age to Éowyn, much to her surprise.
** Possessing the One Ring also slows down aging; for the 60 years Bilbo carries the Ring he does not appear to age much at all (but it catches up with him after he abandons it), and for the 17 years Frodo has the Ring he experiences the same thing.
** Alongside Bilbo, normal Hobbits also age slowly -- Frodo was 33 when he took up the Ring and considered to have only just come of age, while Pippin was 29 during the War of the Ring and is mistaken for an early teenage male. When Aragorn and Legolas ask Éomer if he did not find Hobbits among the slain Orcs, they describe them as small bodied and child-like in appearance. There are many short people in RealLife, but they do not look childlike. By comparison: Frodo is 10 years older than Boromir, and Sam is only two years younger.
** The Ringbearers count as this compared with normal hobbits and Aragorn counts as this compared to other Númenóreans. However, there are humans with normal lifespans in Middle Earth (the average life expectancy of Tolkien's generation was 80, so this should be used as the default).
** The book reveals that Aragorn was granted the ability to choose the time of his death by the Valar, as a reward for his great deeds during the War of the Ring. He ends up living to be 210 years old.
* ''Literature/{{Toradora}}'': Taiga Aisaka, aka [[InSeriesNickname the Palmtop Tiger]], is 17, but is [[TheNapoleon very short]] and [[ACupAngst flat-chested]], which makes her look younger than she really is. [[BerserkButton Point either one out at your own peril]].
* In the ''Literature/TowersTrilogy'', protagonist Xhea is 15 years old but only looks about 12. She believes that her dark magic has stunted her growth, though given her perpetual poverty it's also possible that malnutrition played a role.
* ''Literature/TrappedInADatingSimTheWorldOfOtomeGamesIsToughForMobs'': Yumeria looks like a young girl. She's actually old enough to be a mother. JustifiedTrope - Yumeria is an elf, and all elves look younger than they actually are.
* ''Literature/{{Twilight}}'': Being vampires, all of the Cullens are at least 80 years older than they look, ranging from OlderThanTheyLook for the youngest to Really700YearsOld for the oldest.
* Charlotte B. Lord, the school principal of Midgar in ''Literature/UnlimitedFafnir'', looks like a 10-year-old girl. Yuu, at sixteen, is much taller than she is as well.
* ''Literature/{{Uprooted}}'': [[WizardsLiveLonger Wizards live for centuries]] and show no signs of ageing for most of their lives. At 150 years old, TheArchmage Sarkan looks like a man of twenty, except for a disconcerting timelessness in his eyes.
* Due to her short height, a 16-year-old Mia Rinaldi from ''Literature/VampireAcademy'' still looks 11 years old.
* ''Literature/VanasHeritage'': Nirvy is almost fourteen at the start of the book, but gets mistaken for much younger, because of her being very short and flat-chested.
* ''Literature/TheWanderingInn'':Although Ceria looks to be in her 20's, she actually is 40, but her elven blood allows her delay the aging process.
* [[BigBad Scourge]] of ''Literature/WarriorCats'', mostly because of his small size. Firestar even mistakes him for an apprentice at first. His name was Tiny when he was a kit, to emphasize this further.
* ''Literature/TheWaterAndTheWild'': [[TheProtagonist Lottie]] is 12 years old, but she looks 6. [[spoiler:This may have to do with her being half-sprite]].
* This is deconstructed in a poem titled, ''White Lie'', where the subject, trying to evade someone making advances on her, tells him she's underaged, which convinces him to leave her alone, as she looks young enough to pass as such.
* At the SuperheroSchool Whateley Academy in the ''Literature/WhateleyUniverse'', Generator (Jade Sinclair) and Warlocke are both fourteen, but look only ten or eleven. Then there's Headmistress Elizabeth Carson, who looks like a hot movie starlet in her early thirties, but is actually over seventy. And there's at least one teacher there who's Really700YearsOld: Circe. [[Myth/GreekMythology The Circe.]]
* Nancy has just turned 32 at the beginning of ''Literature/WhereAreTheChildren'', but several people comment that she looks much younger, particularly because she gives off a reticent, vulnerable air. Her husband Ray mentions that although he's only a few years older than her, he "always felt infinitely her senior". Even in her twenties, she looked more like a teenager. Unfortunately, the fact Nancy hasn't physically changed much (besides dying her hair) in the past seven years makes her easily recognisable to people who see old photos of her from her murder trial. [[spoiler:It's also revealed her first husband was attracted to her specifically ''because'' she looked and acted young for her age, including making her wear [[AgeInappropriateDress childish-looking dresses]] that accentuated this]].
* ''Literature/WildCards'' has this with several characters, most notably the Golden Boy, Jack Braun. Possessor of NighInvulnerability, he's an original, who gained his ace powers when the virus was first released in 1946, and is near immortal. Also applies to the Sleeper, Croyd Crenson (Also an original, though since his appearance is altered every time he wakes up how much this applies is debatable), and Dr. Tachyon, who is described as looking like a man in his 20's or early 30's, despite being in his 80's (The Takisian species ages differently from humans).
* ''Franchise/TheWitcher'':
** Geralt of Rivia, the titular character. Reading between the lines, you can see that he is well into his eighties, and has white hair, though the latter is a side effect from the treatments to make him a Witcher. However, the mutations he has been exposed to and his active lifestyle give him the appearance and physique of an extremely fit man in his mid-twenties.
*** His looks are actually inconsistent between the books and the games, varying from late twenties to mid-forties, but he's still always look younger than his real age, which is pushing one hundred by the third game.
** Geralt's friend, chronicler and drinking buddy Dandelion has been described as being forty, sounding like he's thirty, looking like he's twenty and acting like he's ten. In the games he's in his fifties, but looks like mid-to-late thirties.
** TheEmperor Emhyr is in his sixties in the third game, but looks about twenty years younger than that.
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