Yes, the maximum penalty for possessing a tiny amount of pot is a fine of $100. But if you're a juvenile, the state can also "ground" you (i.e., command "home supervision") for 45 days and make you do "chores" (i.e., spend eight days in the Juvenile Work Project program) as well. So holds the Court of Appeal.
Like many things in life, some privileges come only to adults. Even the privilege to conduct illegal acts with little consequence.