# act one's age, not one's shoe size

idiom

Source: https://englishreference.com/idiom/act-ones-age-not-ones-shoe-size
Updated: 2026-08-10

## Meaning

Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).

## Examples

- Please stop acting your age, not your shoe size.
- The teenagers were throwing food in the cafeteria, so the teacher told them to act their age, not their shoe size.
- Despite his professional title, he continued to make immature jokes during the board meeting, prompting his colleague to suggest he finally act his age, not his shoe size.

## Origin

In reference to a person's shoe size (in the US or UK shoe size systems) usually being much lower than their age.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.