Brake rotors should easily last at least 100,000 miles on a vehicle before needing to be replaced.
However sometimes they may not last as long if you do a lot of stop and go driving or you let brake pads wear down to the metal and then the brake pads mesh with the rotors causing metal on metal which can wear down and damage the rotors faster.
If you notice a squealing noise coming from your wheels when you press down the brake pedal when coming to a stop then your brake pads are likely worn down and need replaced.
You should also hear a metal on metal sound when your brake pads are nearing the end of their life since there's a little piece of metal made onto the brake pads that touch the rotors when your brakes get worn down and need replaced.
When you hear that sound you need to replace the brake pads which usually happen by 30,000 to 60,000 miles but could be sooner if you do a lot of stop and go driving.
I usually replace my brake rotors every other brake pad change just to be safe because your brakes are a very important part of your vehicle and what allows you to come to a complete stop in a timely and safe manner.
Your tires are also a very important part of your vehicle that shouldn't be ignored.