act one's age(redirected from act their age)
act (one's) age
To act in accordance with one's expected level of maturity. Really, John, act your age a little, you're like a child sometimes. I'm glad that Sarah is so committed to her studies, but sometimes I wish she would act her age and go out with friends a bit.
act one's age
Behave more maturely. Although the phrase often is used in asking children to act in a more grown-up fashion ( Only babies suck their thumbs; act your age), it also may refer to an adult who is, sometimes deliberately, acting much younger than might be considered appropriate ( Grandpa, it's time you stopped climbing ladders and acted your age).