Minors aged 16 or 17 who are charged with crimes could sometimes be treated as an adult.In all 29 states and 7 union territories, a minor is referred to as someone under the age of 18.

Things that persons under 18 are prohibited from doing include sitting on a jury, voting, standing as a candidate, buying or renting films with an 18 certificate or R18 certificate or seeing them in a cinema, being depicted in pornographic materials, suing without a litigant friend, being civilly liable, accessing adoption records and purchasing alcohol, tobacco products, knives and fireworks.

The rules on minimum age for sale of these products are frequently broken so in practice drinking and smoking takes place before the age of majority; however many UK shops are tightening restrictions on them by asking for identifying documentation from potentially underage customers.

In many countries, including Australia, India, Philippines, Brazil, Croatia, and Colombia, a minor is defined as a person under the age of 18.

In the United States, where the age of majority is set by the individual states, minor usually refers to someone under the age of 18 but can, in some states, be used in certain areas (such as casino gambling, handgun ownership and the consuming of alcohol) to define someone under the age of 21.

Although in the context of alcohol or gambling laws, people under the age of 21 may also sometimes be referred to as "minors".

However, not all minors are considered "juveniles" in terms of criminal responsibility.In the criminal justice system in some places, "minor" is not entirely consistent, as a minor may be tried and punished for a crime either as a "juvenile" or, usually only for "extremely serious crimes" such as murder, as an "adult".For all provincial laws (such as alcohol and tobacco regulation), the provincial and territorial governments have the power to set the age of majority in their respective province or territory, and the age varies across Canada.For example, in some states a parent or guardian must be present during police questioning, or their names may be kept confidential when they are accused of a crime. Constitution, ratified in 1971, granted all citizens the right to vote in every state, in every election, from the age of 18. In any event, they only separated three of more than a dozen detainees under 16 from the adult prison population.For many crimes (especially more violent crimes), the age at which a minor may be tried as an adult is variable below the age of 18 or (less often) below 16. The court's 5–4 decision was written by Justice Kennedy and joined by Justices Ginsburg, Stevens, Breyer, and Souter, and cited international law, child developmental science, and many other factors in reaching its conclusion. Several dozen detainees between sixteen and eighteen were detained with the adult prison population.Driving certain large vehicles, acting as personal license holder for licensed premises, and adopting a child are only permitted after the age of 21.