It depends on the purpose.
What you might be looking for is Age of Majority.
The age of majority is the threshold of adulthood as recognized or declared in law. It is the moment when minors cease to be considered such and assume legal control over their persons, actions, and decisions, thus terminating the control and legal responsibilities of their parents or guardian over them. Most countries set the age of majority at 18. The word majority here refers to having greater years and being of full age as opposed to minority, the state of being a minor. The law in a given jurisdiction may not actually use the term "age of majority". The term typically refers to a collection of laws bestowing the status of adulthood. The age of majority does not necessarily correspond to the mental or physical maturity of an individual.
Age of majority should not be confused with the age of maturity, age of sexual consent, marriageable age, school-leaving age, drinking age, driving age, voting age, smoking age, gambling age, etc., which each may be independent of and set at a different age from the age of majority.
Although a person may attain the age of majority in a particular jurisdiction, they may still be subject to age-based restrictions regarding matters such as the right to vote or stand for elective office, act as a judge, and many others.