Originally Posted by
Kmxu
Bold mine,
OP, we do not know your travel date and route. In general, mileage ticket for your teen does not have the penalty/restrictions of two one-way cash tickets in terms of air fare. If you do not have enough miles, sign up a UA/Chase credit card and use the bonus miles for the outbound one-way ticket. Mileage ticket is fully refundable/changeable.
Often, buying points and getting a saver award can be cheaper than buying a OW, and sometimes cheaper than buying RT for cash. Especially if there is a bonus points offer.