It is not just mileage, but age that counts for when your belts should be changed. You need to change your belt, and probably should have done so before now. Consult your owners manual for exact intervals, as they can vary by model and year of production. Do not wait until you can perceive a problem - often people do this to perceive if a belt is still good or not. The only way you can tell is if you physically inspect the belt. A broken timing belt can cause severe damage to your engine, including fashioning some new holes in your cylinders via your out of control pistons. Don't risk it, get the belt changed.