A:AnswerTo sign a contract or finance/lease agreement for any phone you need to be 18. Even most prepaid phones require a debit/credit card to set up the account. Even if you're under 18 and somehow have over $1,000 to buy a phone, you still need to have a debit/credit card to set up an account with the carrier (AT&T, Verizon, Cricket, whatever phone service providers are in your area) and to have a debit/credit card on your own, you'll need to be 18 to have THAT account.
But the simple answer is: if you have the cash, you can buy the phone at retail price. It's still best to be 18, stores legally have the right to refuse service if they have a good reason, and most will be nervous about selling a $999 phone to a child that has that kind of cash without ever having had a job. I don't know you or your situation so I can't guarantee anything.
A:AnswerYes, sort of. Any app that normally uses Touch ID can enabled to be used with Face ID, so you will not lose this feature. It will simply be you looking at your phone vs using your finger to log in.