act one's age

Translations
вести себя согласно возрасту
He needs to act his age and stop playing childish pranks.
Ему надо вести себя согласно возрасту и прекратить устраивать детские выходки.
Definitions
To behave in a manner appropriate to one's age, typically used to advise someone to stop acting immaturely or childishly.