When you are not behaving or saying as expected for your age, do others say "act your age"? What other expressions are there similar to this?
Uncle:Isn't this a scrambled egg?
nephew:Yes, it is. Is there anything wrong?
Uncle: I only eat fried eggs for breakfast. I don't eat any other.
newphew: Oh, Uncle Dan, please act your age.
Oh, grow up.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.