Prices vary from company to company. It is usually determined by claim experience over time, but with all factors being equal, a female between the ages of 18 and 25 will generally pay less then her male counterpart. This is because generally speaking younger women have fewer accidents and moving violations than males in the same age group.
Some of the reasons that this is the case is because males on average drive more then females. And if you drive more then your odds of being in an accident increase. Also, young men are more often risk takers behind the wheel. This often results in moving violation tickets. Both of those factors result in higher premiums.
Gender does affect your rates, because statistically females drivers have less incidents than males. Just like location (except in California), marital status, and driving history affects your rates.
Now for the good news, most insurance companies recognize that because you did drive more as a young man that when you are a bit older and your driving experience grows, you can look forward to paying less than women. This is especially true if you have a good driving record and no claims.
To find out the difference in price for a man or woman go here. Our car insurance quotes are always free.