It depends on where you live, how you drive the car, whether it's gas or diesel. Generally, cold weather and/or short trips are bad - they permit condensation inside the exhaust system, which rusts it from the inside out. Gasoline engines are harder on exhaust systems as well. As a reference, my former (now owned by a friend) 1984 300D still has the original factory front and center exhaust sections, though the tailpipe section with the rear muffler has been replaced. That car has more than 250K miles on it! My 1987 300TD had the entire original exhaust system when it was replaced under the trap-ox recall; that was in 1999.