Life expectancy of the timing belt.

With the advance in technology, timing belt can last a very long time.  Life expectancy of the timing belt depend on many factors other than just mileage and age 1) Weather play a very important role, rubber tend to get hard and stiff when it's cold, initial start up under this condition is very hard on the belt, if the vehicle is operate in warmer  climate condition the timing belt will last significantly longer respectively.  if the vehicle was driven in a cold climate condition but kept indoor when not in use, initial start up will also be less severe thus belt will last much longer. 2) Driving habit, timing belt is under greatest stress at inital start up when the belt is cold and stiff, the belt is also under greatest load at the initial crank and inital pick up therefore life expectancy can greatly differ compare to vehicle that is driven in the city as oppose to vehicle that is operating mostly on highway. Timing belt belt is under greatest load at initial acceleration, hard acceleration will put more tension on the belt causing it to stretch and fatigue thus shorten the belt's life.  3) Contamination with oil and coolant on the timing belt can greatly affect life expectancy of the timing belt.
Life expectancy of the timing belt depends on many factors other than mileage and age, it depend also on weather, storage condition, driving habit and contaminant.  Car manufacturer are very conservative when recommend replacement interval, everyone driving habit is different, every vehicle is subject to different condition.  Car manufacture have to be conservative when recommend a replacement interval, one vehicle's belt break out of a million before the recommended interval is enough to tarnish there reputation, one must expect the manufacture to be conservative in their recommendation. Many people don't replace their timing belt pass 300000 km, we actually came across a 96 Corolla with 665000km on original timing belt, it was sold after that.  This is no to say all timing belt will last that long, but just point out that life expectancy of the timing belt greatly varies by driving habit, weather, storage, engine condition.  It's best to have the belt inspected.  Inspection is definite possible with proper equipment and knowledge.