I suspect sidewalk riding, if over the age of 13 or so, is illegal in most cities and suburbs in California. I haven't done a survey, but it's true for my town and true for San Francisco.
There are very good reasons for a bias against cycling in pedestrian spaces, and I'll just leave it at that. Frankly, I am against "protected" bike lanes as well, I'll take my chances with the grown-ups.
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There is more to life than simply increasing its speed. - Gandhi