If you’re having brake problems (grabbing, pulling, vibration, noise, etc.) it is always a good idea to have them checked. Otherwise, there is no specific time period for how often brakes should be replaced. It all depends on the driver, the driving conditions, the weight of the car, the brake system itself, and really anything else you can think of. Have your linings looked at; there is a minimum acceptable thickness that applies to your vehicle.
If you are hearing more than a little bit of noise (due to the metal nature of brakes now, a little noise is normal) such as grinding, screeching, growling or chirping, it could be time. If your brake pedal seems to be sinking faster and faster into your car, that could be a good indicator too. Since we live in such a hilly area, our brakes tend to wear down faster than they would in flat place. Stop-and-go driving also does a number on brakes. If you are questioning it, it’s a good idea to have them checked.