of age
- be at level of full maturity, or maturity sufficient for an activity
Wiktionary
prep_phrase
- Old enough to be considered an adult (in law, or by society generally).
“He's of age now: he can make his own decisions.”
- Having existed for a certain period of time; used in referring to a person's age.
“He has a son who is six years of age.”
“One must be 18 years of age to be an eligible voter in most countries.”