Kids should get their own car insurance when they purchase and title their own car and no longer live at home. Although some insurance companies will let you add a vehicle not registered in your name to your policy, most will only allow cars titled in the name of the primary policyholder to be added.
If your child lives with you, it's assumed they have regular access to your vehicle, and most insurers will require them to be listed on your policy. As soon as your teen driver is licensed, you'll need to add them to your policy or prove to your insurer that they are either insured or permanently residing elsewhere. If you title a car in your child's name, your child will have to get their own policy. But you can still list them as a driver on your policy if they are living at home and will have access to your covered vehicles.
There is no set age at which you have to remove your child from your car insurance policy. They can remain on your policy indefinitely, as long as they live at your address and the title remains in your name. It is possible to exclude your child from your insurance policy, but that means your child has zero coverage if they get into an accident driving one of your cars. If your child has had multiple tickets, a license suspension or a DUI, your insurer may require you to exclude your child from your policy.
Having a young driver on your policy has drawbacks for you as the primary policyholder. The biggest disadvantage is that your child's driving habits become part of your insurance history, since your policy will pay for their claims. If your child gets into an accident, you will see premiums go up for everyone listed on the policy.
On the bright side, it is more cost-effective to add your child to your policy. Teenagers will get a more affordable rate if they are listed as a driver on a parent's policy than they would on their own policy. Plus, you're eligible for discounts your child might not be, like bundling with homeowner's coverage. Although car insurance for teens is always expensive, you may be eligible for additional discounts if your child has good grades, attends driver education courses, or takes a defensive driving class.