Minor (law)

In the law, a minor is someone who has not yet reached the age of majority. In most countries, a person becomes an adult at age 21, therefore, a minor is a person who is 20 years old or younger. 
"Minor" can also mean a person who is not old enough to do a particular activity, for example, while 21 is the age of majority in the United States, the minimum age to buy alcoholic beverages (such as beer, wine, and liquor) in the United States is 21 so in this context, a minor is a person who is 20 years old or younger.