Ludacris flew from LAX to ATL with his 13 year old daughter and then left his daughter in the club to await her connecting flight to NYC. Then Delta called him to say she couldn't board her flight as she was an unaccompanied minor and no $100 fee had been paid. He pissed and moaned and eventually returned to ATL, paid the fee and she was put on the next flight to NYC in First Class:
http://www.mercurynews.com/celebrities/ci_26285863/why-ludacris-left-teenage-daughter-alone-at-airport
http://www.tmz.com/2014/08/06/ludacris-leaves-daughter-airport-karma-delta-flight/
UA and AA permit 12 year olds to fly alone without paying the unaccompanied minor fee - AA lowered their age a few years ago from 14.
http://www.mercurynews.com/celebrities/ci_26285863/why-ludacris-left-teenage-daughter-alone-at-airport
http://www.tmz.com/2014/08/06/ludacris-leaves-daughter-airport-karma-delta-flight/
UA and AA permit 12 year olds to fly alone without paying the unaccompanied minor fee - AA lowered their age a few years ago from 14.