The United Airlines Unaccompanied Minor Policy allows children to travel without a parent or guardian under supervised care. Children aged 5 to 14 must use the service on United flights, while teens aged 15 to 17 may use it optionally. Parents or guardians must book through United’s reservations team, complete the required paperwork, and pay the applicable service fee for each trip.
https://www.flyviago.com/unaccompanied-minor/what-is-united-airlines-unaccompanied-minor-policy/