This varies depending on the type of material used. Proper installation and regular maintenance also affect the lifespan of your gutters and downspouts. Here are some estimates from the International Association of Certified Home Inspectors:
20 to 40 years for aluminum gutters and downspouts.
50 years for copper gutters and 100 years for copper downspouts.
20 years for galvanized steel gutters and downspouts.
25 years for vinyl gutters and downspouts.