I have to disagree extremely strongly with the fact that UMs should not be allowed to fy unaccompanied.
Lots of my uncles and aunts live in Spain & Greece and so from the age of 6 I used to fly with British Airways, Iberia or Olympic from Heathrow to visit my family.
At bmibaby we used to accept unaccompanied minors from thw age of 11, however we gave them no assistance, I do not agree with letting 11 year olds running around an airport by themselves cause they'll get lost easily!
Now its 15, but I dont think you should not let UMS not fly.