I believe (but don;t quote me on it!) that the name on the AP and the room reservation must be the same. That tells me that it must be an adult AP since the person reserving the room is supposed to be 18+ YO.
However, I have seen posts around here of people buying their child and AP and getting the discount. Personally, I would get clarification before doing anything. I'd hate for you to get to WDW and not be able to get the discount!