Rule of thumb on Timing Belts, 6 years or 70,000 miles for scheduled replacement or inspection. Some are designated as "Interference" which means if there is a timing fault, there Will be Damage to motor. A "Freewheeling" designation means if the belt breaks, damage to motor is unlikely. Some have an internal waterpump driven by the timing belt. Pulleys, tensioner, waterpump, need to be inspected for possible replacement.