Brake wear isn't related to how many miles you drive but how the brakes are iused. If you track the car or drive it hard on the road, the brakes won't last as long as if you are doing lots of interstate driving. A lot of stop-and-go driving will wear them faster as well.
How are you determining that the rotors and pads are worn out? If the pad wear indicators aren't on, have you measured the pad thickness? The only way to determine if the rotors are worn out is to measure the thickness or if you have cracked them.
You mentioned you have a friend who has serviced the brakes. What exactly has he done? They don't need much maintenance other then a fluid flush every two years if you aren't tracking the car, so I doubt he could have done anything to them that would cause abnormal wear.
Karl
