Yes, 16-year-olds can fly alone on United Airlines, and they are generally treated as "adults" for the purposes of air travel. United's Unaccompanied Minor (UM) service, which provides specialized assistance and supervision, is mandatory only for children ages 5 through 14. For young adults ages 15 to 17, this service is entirely optional. If a 16-year-old flies without this service, they simply book a standard ticket and navigate the airport and connections independently. However, if parents prefer the extra peace of mind, they can choose to pay the unaccompanied minor fee (which is typically around $150 each way), and the airline will provide a staff escort to guide the teen through the airport, assist during connections, and ensure they are met by a designated guardian at the destination. It is also important for minors traveling internationally to carry a notarized letter of consent from their parents.