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).

In addition to the idioms beginning with act

• act of faith
• act of God
• act on
• act one’s age
• act out
• act up
• act upon

also see:

• catch in the act
• clean up (one’s act)
• do a disappearing act
• get in the act
• get one’s act together
• hard (tough) act to follow
• high-wire act
• in the act of
• put on an act