[[quoteright:200:[[Film/AnchorsAweigh http://static.tvtropes.org/pmwiki/pub/images/young_aunt_a_pleasant_surprise.jpg]]]]
[[caption-width-right:200:[-Not the kind of aunt they thought.-] ]]

Characters assume another character's age, often based on common assumptions of traits that character has, or there can be other reasons.

A common one is an aunt. In many cultures aunts are thought of as old (and [[ObaSan can even be offensive in Japan]]), so when the aunt turns out to be only a few years older than the niece/nephew, it can be quite a surprise.

Compare TomboyishName, ExpectingSomeoneTaller, ActuallyThatsMyAssistant, OlderThanTheyLook, YoungerThanTheyLook, AgeInappropriateDress.
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!!Examples:

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[[folder: Advertising ]]

* The Grape Nuts cereal television ad: "[[http://www.youtube.com/watch?v=3UnJSTpHsXc Mrs. Burke, I thought you were Dale!]]"
** Later followed by the Palmolive "Which hands belong to the daughter?"
* One ''Oil of Olay'' commercial had a stage psychic guess a woman's age, and undershoot because she was using the product. She plays along, and says the psychic was correct.

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[[folder: Anime and Manga ]]

* In ''Anime/DennoCoil'' Haraken's aunt, who is referred to offhand as being the commander of the Satchiis, is assumed by the main characters to be at the very least middle-aged. When she finally appears, it turns out that she's actually on the nearer side of twenty.
* This is actually Maria of ''Manga/HayateTheCombatButler''s {{Berserk Button}}. She continually states that she's 'only 17' while everyone around her assumes she's older because of the aura she puts up, and being Nagi's {{Cool Big Sis}}/Mother figure.
* It's a running gag in the ''LightNovel/{{Baccano}}'' light novels that, despite nearly half the cast being immortal, only Firo (already [[OlderThanTheyLook a bit young-looking]] before immortality) has to deal with the annoyances of not looking his age, such as getting carded at age ninety, being detained for claiming he was seventy on his passport, and constantly being called 'babyface.'
* The protagonist of the first story in ''Himitsu Kichi'' mistakes a sixth grader for a college aged student. In turn he mistakes her for a kid his age when she's 16 years old.
* In ''Manga/LuckyStar'', Miyuki's mother looks so youthful and cute that she's actually often mistaken for her older sister rather than her mother.

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[[folder: Comic Books ]]

* In the ''ComicBook/FantasticFour'', the Thing frequently mentioned his 'Aunt Petunia', with the implication that she was an old woman. When she finally appeared in the comic during Creator/JohnByrne's run, Petunia (she prefers 'Penny') was revealed to be his uncle's second wife and an attractive woman about the Thing's own age.

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[[folder: Film ]]

* In ''Film/AnchorsAweigh'', two Navy sailors take a runaway kid back to his home, where he lives with his aunt. They think she must be old, and are surprised that she is about their age.
* Another younger than expected aunt in ''Film/AFewGoodMen''.
* In the ''Literature/BabySittersClub'' movie, the parent of one of Stacey's baby-sitting charges warns her in advance that her "little cousin" from abroad will be home when she comes by to baby-sit. She brings with her a little American flag to give him, expecting a young child. Instead, he's an extremely attractive 18 year old.
* In ''Film/IndianaJonesAndTheTempleOfDoom'', Willie Scott dresses up beautifully for the dinner at Pankot Palace in hopes to impress the wealthy Maharajah. She's chagrined when he's revealed to be a kid around the same age as Short Round.

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[[folder: Literature ]]

* In MaryRenault's ''The Last of the Wine,'' the main character's lover has a spazz attack when he realizes that the woman the main character has been calling "Mom" for the whole book is a stepmother and about the older lover's age.
* Early in ''[[Literature/AuntDimity Aunt Dimity: Detective]]'', Lilian Bunting asks Lori to entertain her nephew "Nicky" while she and her husband attend Prunella Hooper's inquest. Lori expects to receive a visit from a small boy, and is surprised when thirty-something Nicholas Fox introduces himself.

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[[folder: Live Action Television ]]

* It's never explicitly stated what Niles expected in ''Series/{{Frasier}}'', but he is clearly surprised the first time he meets Daphne, mentioning that Frasier told him she was English and um, well... He most likely assumed she was a stuffy older lady.
-->'''Niles:''' ''You're'' Daphne?
* In an episode of ''Series/{{ER}}'' an injured toddler comes in and shouts that Uncle Charlie hurt him. Someone asks if they should call Social Services only for someone else to point at another, unharmed but still grouchy, toddler, and say "That's Uncle Charlie".
* In an episode of ''Series/UnitedStatesOfTara'', Kate's boyfriend is about to meet Kate's family, and Kate had previously mentioned that she had a younger brother. Kate's boyfriend buys a toy train, expecting that he'll be quite young, except Marshall (Kate's brother) is in his teens, causing an awkward interaction.
* In an episode of ''Series/{{Firefly}}'', Mal invokes this trope to evade INeverSaidItWasPoison, when asked whether he has seen fugitives, "a brother and sister", by pretending to assume that the pair in question were children, when he actually knows exactly who and where they are.

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[[folder: Professional Wrestling ]]

* [[WrestlingFamily Eddie and Chavo (Jr.) Guererro]] were close enough in age to be brothers (2 years apart), but they were uncle and nephew.

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[[folder: Web Comics ]]

* In ''Webcomic/TowerOfGod'' this happens commonly since the Shinsoo atmosphere slows down and sommetimes even stops aging. This leads to cases of Ship Leesoo being in his late twenties and Yeon and Hatsu in their late teens whereas Androssi is about 300 years old and her "niece" Anak is even older.
* A RunningGag in ''Webcomic/HannaIsNotABoysName,'' as one of the few things that seems to really aggravate [[ThePollyanna Hanna]] is when people mistake him for a teenager. ("'''''I'm 24.'''''") He certain [[OlderThanHeLooks looks young]], but it's never made clear if that has a [[AmbiguouslyHuman supernatural basis]] or if he's just naturally scrawny.

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[[folder: Western Animation ]]

* In ''WesternAnimation/AlvinAndTheChipmunks'', Alvin hears about having an oldest fan, and thinks she's just in her twenties, while she is actually a senior citizen.

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