Well, for the ones that dont know, it doesn't just depend on your age and car...most monitor the following:
Night Parking Status (Garage, Carport, Street, etc)
Geographical Location (if you're in a city or country, what the local crime rates are, accident statistics, etc)
Specific Vehicle Statistics (Avg of accidents for that type of vehicle)
Engine Size and/or Induction type
Type of insurance (private/pleasure, commuter (distance variable), or business)
policyholder'* credit rating
name on registration and title
Then theres the discounts, such as...
Multiple Vehicle Policy
Engine Immobilizer (Active or Passive security system)
Active or passive restraint
Airbags (front, front side, front side curtain, rear side, rear side curtain, knee, etc)
etc etc depending upon the company
then of course, your deductibles, coverage levels, etc.
just a little info for the ones who wonder. those who know, correct me if i'm wrong :P