The original OP said something about could they book a 'holiday' for the 16 year old and would the OP as an adult (and on a separate flight only booking) be able to check into the room - because they actually needed the room and not as a ploy to simply reduce the price - thus meeting the need to have someone over 18 in the room.
OP has not helped themselves to get accurate answers by changing the entire premise of the post.