Legal Question in Insurance Law in California

In America, anybody can sue anybody simply by filing the complaint in an appropriate court and/or serving the other party with appropriate legal process, depending upon the jurisdiction's local law. Suing someone does NOT mean that the person bringing suit is entitled to recover. So long as the person sued answers the complaint on time and defends, the burden is on the person bringing suit to prevail. And that's not necessarily easy.

If you are asking whether there is any basis for suing your parents in the particular circumstance, that would depend on the facts.

If as you say you are 21, have your own job, own your own car, and insure it yourself it would seem that normally there would be no basis to sue your parents just because you happen to live at home.

However, should you negligently injure someone while driving your own car, with your own insurance, while you would have primary liability, that does not mean that other thrid parties may not also have liability under certain circumstances.

For example, if you were driving the car while doing errands for your employer as part of your job at the time of the accident, your employer might have liability for your negligence. Similarly, if you were deemed doing errands for your parents, such as dropping off their laundry or buying groceries for them or the whole household, you might well be considered to have been acting as the agent of your parents. In that case your parents could have liability for your actions as their agent.

Your insurance company, and if they have coverage, your parents insurance company should defend them.