Car insurance rates vary greatly depending on age. Your risk profile as a driver will change throughout your life, so you may be eligible for discounts at some points in your life while other times you may see your car insurance premium increase. This is why you want to keep shopping for car insurance throughout your life so you ensure the best value.
Companies do not have a standard rule as to what is considered high risk. If you have had an accident or moving violation the variance in premium will differ from company to company. You may have to get several quotes before finding the company that will work with a poor driving record. If you are diligent, then you should be able to find a rate you can live with.