The answer to that question hinges on several variables, including how many miles a vehicle is driven, on what kinds of roads it's driven, and whether it's driven gently or with abandon.
Those variables make it virtually impossible to assign a number of years or miles as a broad stroke, though we would expect shock absorbers (or struts on vehicles with strut-type suspensions) to last at least four or five years, unless the vehicle has been subjected to extreme use. It's also not unusual for shocks to last 10 years on a vehicle that has lived most of its life on smooth pavement.
On the other hand, rough roads marked with potholes, large cracks and sharp ridges that run across the pavement (the typical urban torture test) will wear out shocks faster. Frequently carrying heavy loads or driving on unpaved roads with deep divots or imbedded large rocks will do the same. If you're the type who takes bombed-out roads at the same speed as fresh asphalt, that devil-may-care approach is bound to exact a toll over time. Winter weather and road salt can also shorten shock absorber life by contributing to corrosion.
