I started riding one of these things when I was like 13.... cant say I had the best judgement. I was actually pretty decent - but got caught running through a stop sign by a motorcycle cop. (but officer I have to stay @ full throttle through the stop sign to make it up the hill on the next block...) He was very nice and let me off with a pretty stern warning - but I could tell he liked my bike. Now I always stop etc.
Im about to turn 16 and be officially "legal" To be honest cops around here (san francisco) really dont give a crap - there are crazy moped tuners blasting through traffic at like 40mph all the time and they barely turn a head. Pedal bikes rarely even stop at stop signs on the city bike routes (I never do - and im often riding with a group of 10 or more other bike commuters) and the cops never bother you about that. Not to mention the tendencies of people here to smoke weed in front of cops.... crazy city. Seriously - i go to school right by the famous Haight street - but to be honest its just a bunch of crack heads that will try to break your u lock to steal your bike. Ok enough rambling.... MoTo
EDIT: THIS is the kind of crap people pull in san francisco: http://www.craigslist.org/about/best/sfo/27499971.html