Adulthood in the eyes of the law. After reaching the age of majority, a person is permitted to vote, make a valid will, enter into binding contracts, enlist in the armed forces, and purchase alcohol. Also, parents may stop making child support payments when a child reaches the age of majority. In most states the age of majority is 18, but this varies depending on the activity. For example, in some states people are allowed to vote when they reach the age of 18, but can't purchase alcohol until they're 21.