Am I an unaccompanied minor?

You and your sister do not have to be 'official' unaccompanied minors unless you and or your parents want you to be. You are both old enough to travel without an adult. The upside of traveling without airline supervision: you don't have to wait in a designated area and be escorted by airline personnel; you don't have to wear 'embarring' tags around your neck. The downside: in the event of a delay, cancellation,reschedule,etc. you may not get the extra attention and privileges that a minor child who is traveling with unaccompanied papers will have. Many parent's don't mind paying the surcharge for the extra peace of mind.