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Twelvies are (usually) 11-13 year old kids who, essentially, think they're more important/grown up than they really are, when actually these attempts at being more 'cool' and 'mature' just make them look less mature to those who actually are. They're quite naive and act like they know everything, when in fact, they don't. They often overuse stupid words such as 'swag'.
Twelvie: Look at me, I've got a boyfriend, I'm practically an adult now. Swag.
by ShelleyKnowsAll February 20, 2014
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2
A person that is of the age 12. They think they're top sh*t. They think they own the place. They think they can win fights. They think they can do whatever they want. They act like there 16.
Wow that kid is such a twelvie.
by Sarcasmm Queen April 07, 2015
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Twelvie: Another word for a person between 12-15 years of age who is either a massive ganga/slut or who is a scooter fag who thinks they are cool by rollin round in big groups of other twelvies. ( Wannabe bikies )
Kids who think they are tough rollin around with their friends on scooters.

Non-twelvies talking:

Dude1:That girl over there was tunin on Jackson the other day.
Dude2:She was grindin on me at Sensations....
Dude1: LAWL fuckin twelvie ganga.
by Paul Schemier June 08, 2011
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4
Someone who does Music.ly, or someone who is just too cringe to handle
Jason is such a twelvie, just look at his music.lys
by Bananasinpjs March 29, 2017
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5
A word used to describe any teenagers between the ages of 12-18.

Anyone who is under the (Australian) legal age.
Person 1: I can't tell how old these girls are with all their makeup.
Person 2: Oh, she's a twelvie trying to get in a club.

Person 1: So many twelvies around.
Person 2: It is school holidays.
by Squisheee October 26, 2014
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A twelvie is a 12yo girl or boy that acts way older than they actually are, and acts ridiculously annoying. They also try to be cool, but epicly fail.
*12yo buys car*
"Such a twelvie.."
by COOKIEWOOKY October 03, 2019
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7
a person of the opposite sex who is noticeably younger than yourself, often caught checking you out. Usually they appear to be twelve years old, hence the term twelvie.
That twelvie over there was totally checking you out. You're old enough to be his aunt or something.
by mllelanoir August 30, 2007
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