If you are 16 years old and on your mom's insurance plan, but you drive your grandma's car, you would still be covered under your mom's insurance plan. As a dependent under the age of 26, you are generally able to remain on your parent's health insurance plan, regardless of whether you live with them, are claimed as a dependent, or have a full-time job. The Affordable Care Act allows young adults to stay on their parent's plan until they turn 26. This coverage would extend to you driving your grandma's car, as long as you are a named driver on the insurance policy.