The law here sets the limit for sidewalk riding as wheels over 20". Nothing about age of rider. Cars coming out of intersections are not expected to look for anything faster than a pedestrian on a sidewalk. That is why you have to be particularly careful when riding the sidewalk. The closer you are to buildings, or in this case a parked truck, the less time you have to see anything approaching around the corner - so keep well out into the road when approaching intersections.