act your age(穩重一點，不要像小孩子一樣)
A:Mom, I broke the window again.
B:You should act your age.
OrDon't be so childish
Don't trust anyone over 30(別聽信30歲以上人的話)
A:He told me not to go to college.
B:Don't trust anyone over 30. You should stick to your dream
Don't you think you're a little old to be dong(that/this)(做這種事，難道不覺得老了一點嗎)
B:But they're cute.
OrAren't you kind of old for that sort of thing?
Have one foot in the grave(老了)
(be) wet behind the ears(乳臭未乾)
A:Frank said he wanted to find the job
B:What can he do? He's wet behind the ears.
When will you grow up?(你什麼時候才懂事)
A:Let's play a trick on our teacher.
B:When will you grow up?
OrAct your age.