It's the same with children. I hesitate when I think of letting my 9 yr old daughter ride her bike to school (her school is in the neighborhood, no major streets or crossings, quite safe area, etc ,etc). I think it has to do (among other things) with media possibly instilling fear? Honest to God, at that age I was exploring way farther and my parents had way less supervision over me (or siblings).
Or maybe I'm just paranoid.