This might have some relevance:
The age of majority is the threshold of adulthood as it is conceptualized (and recognized or declared) in law. It is the chronological moment when a child legally ceases to be considered a minor and assumes control over their persons, actions and decisions, thereby terminating the legal control and legal responsibilities of their parents or guardian over and for them. The word majority here refers to having greater years and being of full age; it is opposed to minority, the state of being a minor. The law in a given jurisdiction may never actually use the term "age of majority" and the term thereby refers to a collection of laws bestowing [or recognizing] the status of adulthood. The age of majority is a legally fixed age, concept or statutory principle, which may differ depending on the jurisdiction, and may not necessarily correspond to actual mental or physical maturity of an individual.
In practical terms, there are certain specific actions which a person who attains the age of majority is permitted to take, which they could not do before. These may include entering into a binding contract, buying stocks, voting, buying and/or consuming alcoholic beverages, driving motor vehicles on public roads, and marrying without obtaining consent of others....
Age of majority pertains solely to the acquisition of control over one's person, decisions and actions, and the correlative termination of the legal authority and responsibility of the parents (or guardian(s), in lieu of parents) over the child’s persons and affairs generally.
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The age of majority (in the US, as well as most of the world) is usually recognized as eighteen. The only states that are exceptions, last time I checked, were Nebraska (where it is nineteen), Alabama (nineteen), and Mississippi (twenty-one).