Are you me? :) I used to do this exact same thing in the exact same age range.

This was in the 90s though - what I still regard as the Golden Age of Flying (tm), and the Unaccompanied Minor service offered by most airlines was absolutely fantastic. You would be under constant supervision in the airports, get access to the nicer lounges.waiting areas, have priority for boarding/disembarking, and be generally treated like royalty.

Even if you were flying coach/economy.

It was totally brilliant, and I was heart-broken about losing this aspect of flying when I turned 16. (IIRC that's the age limit)

Come to think of it, the reason that UA screwed the pooch so badly on this could be because of the death of the Golden Age of Flying.