The purchaser of the ticket does not have to be the traveler. No mention in the FAQ about minors.
"The Mileage Plan™ member who owns the companion fare code must either be one of the travelers or the purchaser of the reservation. If the member is allowing two travelers to use his or her companion fare code, then the member's name must match the name on the credit card used to purchase the reservation."
https://www.alaskaair.com/content/mi...-discount-code