In car insurance, children must be removed from your policy by the time they are 25 years old. In order to remain on the coverage for that long, the child must either still live at home and be dependent on the parents or attend a university in another location. Children who are self supporting and live at a different address than their parents are required to get their own auto insurance policy as well.
The reason children under 25 must have their own policy if they live at another location is because different areas of town may have far different insurance rates based on the overall risk factors of crime or traffic accidents. In order to assess the risk correctly, the insurance company needs to know the details about where, when and how far the car will be driven.
In order to keep the costs of insuring someone under 25 down, keeping a solid B average in school will net discounts, along with voluntarily signing up for and taking a driver improvement course. Maintaining a clean driving record is the best way for people of all ages to lower their insurance costs, but risky behavior in young drivers is more costly than for other age groups.
The car insurance standard is 25 in all states, and most states allow for insurance companies to drop listed insured persons if they are no longer living at the same location or dependent on the parents for other support.