If you are trying to find the age limit for flying kids free. Children 2 to 12 years old are considered minors, and kids under 2 years old are infants who can fly free in their parent's lap on domestic flights, but international travel has some changes. Moreover, many airlines provide children aged 5 to 12 years old the ability to fly alone, and they offer fare discounts. For more details about the flight age limit, visit the Airlinesunaccompaniedminor website.