If our society had one then we wouldn't have the "when am I a man" confusion that we do: is it 16 [when you learn to drive], 18 [when you reach the legal age of majority], 21 [when you can drink], 26 [when your car insurance goes down], 40 [when you lose your virginity], or some arbitrary event like moving out?
When were you told you were an adult?
We have degrees of adulthood in this country.