There are several factors to consider when it comes to insurance rates and your age. No one company rates the same. In most cases, females will see a decrease in rates once they turn 21. Males will typically see this decrease when they turn 25. In certain states, such as California, how long you have been licensed continuously (with out a suspension) is a big factor in rates not matter what your age is. Typically, you have to have been licensed continuously for 3 years before you will see a decrease in your rate. Keep in mind insurance rates change based on the cost of doing business (number of claims paid out, cost of repairs to newer vehicles, etc). So while your age may be a lesser risk, this doesn't mean your rates will go down, they just may not increase as much if you are younger. You can get several different quotes online
if you want to see how your age will impact your rate specifically.