Can I be billed retroactively by the insurance company because I didn’t declare my 21 year old son on my insurance policy when he got his license?

If your son has not been involved in an accident in your car, you can simply tell your insurance agent that your son is licensed and add him to your policy effective now. Most insurance companies will not add a driver retroactively unless there has been an incident involving that driver.Even though you had not declared him on the policy, he was covered as a permissive user. Obviously the insurance companies would prefer to add young drivers when they are first licensed, since they can collect the premium for that driver. However, many car owners have done the same as you have done. When you call your agent to add your son, make sure you do indicate when he was licensed. By doing this he will get credit for the time since he was licensed. If the agent asks why you didn’t declare him, simply advise him you didn’t think about it since he rarely drove. If the agent wants to try to backdate the change, tell him you don’t want to do so, just to add him now. The agent should go along with your instructions.