I'm going to be a bit upset if IP and credit card are the trigger. My minor daughter certainly does NOT have her own credit card, lives with me (so obviously I use the same IP to access both accounts), HAS flown on US (her account was several months old when I used it for the shared miles promo, and had pre-existing US miles in it, as did mine), and as her parent, I believe I legally control things like her FF accounts until she reaches her age of majority.