Definition : the age at which a person is granted by law the rights (as ability to sue) and responsibilities (as liability under contract) of an adult compare emancipate At common law, the age of majority was 21. Age of majority is now set by statute, in most states at 18. The age at which a person may perform various acts, as legally drink alcoholic beverages, make a binding contract, or make a valid will, does not necessarily correspond with the age of majority.