To act mature, to act as a 21 year old.
" Stop being immmture, you got to be 21 about it."
by jkk April 04, 2006
Can you define these popular missing words?
To own up to or acknowledge and accept responsibility for actions and/or wrongdoings regardless of the repercussions and opinions of others
" I already know you lying so Be 21 about it."
by URBANEDUCATEDREDNECK March 27, 2016