Legal Question in Civil Litigation in California

With the POA, you can take action to demand the car back and can try to rescind the purchase contract from the dealer as 'voidable'. You could sue to enforce, or you could report to the police elder abuse/fraud by the dealer and the minor. Consult with local counsel if you need help.

It would have to be a very broad POA to allow you to do all the things Mr. Nelson says you can do. And elder abuse cannot be charged for conduct involving a 41 year old. It sounds like you need to be made his conservator. The trouble you face is that a POA gives you powers to act on his behalf, but does not stop him from making legally binding decisions too. Only a conservatorship will do that. I'm not sure if he can be declared retroactively incompetent to manage his finances, but it is worth a try. Mr. Nelson is right that you need a lawyer.