twelve

a person of any age or age group that displays the mental or behavioral qualities of that of a 12-year old. twelve (12) in this definition is used as an adjective rather than the traditional noun (being the literal number '12'). being called "twelve" is never used as a compliment, this is strictly an insult. if "twelve" is used to suggestively address someone who is obviously younger than 12 years of age, they will likely be offended. this term is solely used toward anyone obviously older than 12 years of age, as it signifies lack of experience, common sense, or maturity that should exist in someone of their true age.

Person 1: uranus is my favorite planet. get it? get it??? urrrr anussss
Person 2: bro what are you twelve? go sit down somewhere, man.