Ace Cdn beat me to it. Before a 12 year old could fly unaccompanied with a younger sibling and not use the UM service (i.e. pay the $30 charge). I'm sure that something happened that could have resulted in a catastrophe to instigate this change.
Empress, I'm not sure where you got your link but the statement in the employee info systems was a couple paragraphs long and more comprehensive.