How old are you?

How old are you?

Used as a reprimand to someone who has just said something markedly immature or childish. Do you really have to make so many poop jokes? How old are you? A: "Hey Tammy, how'd your date with Mark go? You guys boink, or what?" B: "Don't be gross, Sarah. How old are you, 13?"
See also: how, old
Farlex Dictionary of Idioms.
See also:
  • whine
  • whine about
  • whine about (someone or something)
  • (someone) started it
  • you, he, she, etc. started it
  • it takes one to know one
  • (it) takes one to know one
  • takes one to know one
  • winky
  • meanies