Not all vehicles have Timing Belts - Some have Chains.
Timing Belts are assigned a replacement interval in both miles and months by the car maker.
Automotive fluids of any type (coolant, motor oil, trans fluid etc.) are the enemy of the Timing Belt. Exposure to these reduces life and causes Premature Failure.
The type of engine you have- free wheeling or interference- makes a difference if your Timing Belt fails.
Free Wheeling- you are disabled but not destroyed. Interference - get your checkbook.
Timing Belts get hard, crack, wear out, lose teeth and wear out on the edges.
When you purchase a vehicle it is important to know if it has a Timing Belt and if it does when it was last replaced.
You should always replace your water pump when you replace your Timing Belt.