A child who is travelling without the accompaniment of an adult over the age of 18 years is considered by the airlines as an unaccompanied minor. In general, airlines have age restrictions (children under 5 years cannot fly alone, children up to 18 can be considered unaccompanied minors (depending on the carrier, the age can vary from 14 through 18 years.) Each airline carries its own restrictions for unaccompanied minor travel. You should always check directly with the carrier to learn their specific rules and regulations.