I'm old enough to know what's up.
 →  나도알건 다아는 나이라구.

[예문]
A:What are you talking about?
  무슨말하고있어?

B:You're too young to know what we're talking about.
  넌너무어려서 말해도 몰라.

A:Come on, tell me. I'm old enough to know what's up.
  말해봐. 나도 알건 다아는 나이라구.