Found this one last week - when booking a Delta Amex companion ticket through Delta.com I found an issue where if the companion is a minor the website won't let you book and provides an error message that states to 'call the unaccompanied minor line' for all unaccompanied minor travel and you can't proceed. If you change the companion's birthdate to make them older the message goes away and you can book the ticket. I got a gold line rep on the phone and booked and had her change the birthdate to the real one so I could lock the tickets in.

Kind of hard to be an unaccompanied minor when on the same ticket with your parent, isn't it? lol.