Am I liable for son's auto accident?

For the other driver to individually collect against you, there would have to be evidence that you negligently entrusted your motor vehicle to your son when you knew or should have know that he was not a competent driver.  While age is certainly a factor, youthfulness is not dispositive.  Absent evidence that your son has a bad driving record, there is little likelihood that you could be held responsible for any amount in excess of your insurance coverage limits. Your son could responsible for the excess, bit the excess liability can be discharged through bankruptcy. If a lawsuit is filed against you and your son, then your insurance company is required to provide you with a defense attorney to protect your rights.