act one's age, not one's shoe size
Proposed by a contributor, not yet supported by evidence.
Meaning · English
Behave maturely, not immaturely
Where it’s used:
Used
Widespread English
Sources & notes
Listed in Wiktionary’s “English idioms” category (retrieved 2026-07-29); definition pending editorial review. Definition drafted by AI (@cf/meta/llama-3.3-70b-instruct-fp8-fast) and auto-approved by rule on 2026-07-30; pending editor spot-check.
Common questions
What does “act one's age, not one's shoe size” mean?
Behave maturely, not immaturely
Is “act one's age, not one's shoe size” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.