Unless your 14-yr-old is A-list, it's pretty much at the discretion of a sympathetic desk agent. They may have some discretion to move you around -- but you won't know what the situation is until you get to the airport.

Per policy, you'd have to pay the full fare difference unless the passenger is A-List . And because the flight times are so close together you may run into logistical snafu's with any checked in luggage and/or running from one standby flight to the originally-scheduled flight.

So show up to the airport early, have your 14-yr-old pack light (i.e. check their luggage in with yours), and cross your fingers the people at the checkin counter are in a good mood.