1 definition by ShelleyKnowsAll
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'.
by ShelleyKnowsAll February 20, 2014