At 19 I highly doubt the FA would have made you inconvenience the passenger beside you and make them move their tray/food out of the way to get your passport from your bag. A verbal confirmation used to be all I needed to get served alcohol on UA when I was 20. 15 is most likely very obvious though. Personally if I was OP I would go with AA as I believe he is more based in NYC than LON (based on his spelling) and he won't have to face the horror of BA fuel surcharges on awards.