There are so many variables here....Metallic brake pads will be harder on the rotors than resin brake pads. Also your riding style and the conditions which you ride under will have some effect on the rotors. I am still using rotors which I have purchased between 15-18 years ago. I use resin pads because they are cheaper and most common in the bike shops around here. I ride all year round which includes snow and road salt and grit. I don't live in the mountains so no downhill rides and no hard braking for me, mostly flat and rolling terrain. I also take it easy on the brakes, I don't slam my brakes hard all the time.