Rating Newest Oldest. Best Answer: The absolute minimum age for flying alone on major airlines in 5 years old. Passengers who are ages 5-14 and are flying alone (without a companion who is at least 15 years of age) are considered Unaccompanied Minors (UM's). Passengers whose ages range from 15-17 are considered Young Adults and do not have to use the UM service, but can if they would like to.