How long will a Timing Belt last in a 1998 Toyota Camry 4 Cylinder?

Any time now. Regardless of mileage timing belts should be replaced every 7 years and yours is nearly double that. Although the engine is not interference, if you don't replace it before it breaks you will be stranded (at least momentarily) when it does break and will have to pay towing, which can increase the replacement from $300 to as much as $500, depending on where and when it fails. It is axiomatic that whenever a car fails you were wanting to go somewhere, and it doesn't matter how important it was.