Rotors can live the entire life of the car. The only reason to replace one would be if it is warped (unlikely with the stock calipers, brake lines and fluid -- you just can't exert enough force before ABS kicks in) or you fail to change your brake pads and actually score or etch the rotors.

We've had threads about this where people have used the stock pads/rotors setup for 90,000+ miles. Rotors have no "expiration date" and whomever told you this was clearly more concerned about selling you a new set of rotors than your safety or technical knowledge.

 

In theory it can be done, but you'll be hard pressed to find a shop that'll agree to do it. Using the standard practice, turning a slotted rotor will destroy the re-finishing bit, so many shops (I'd be willing to say 99%) won't turn the rotors for you.

But, you don't have to replace the rotors when the pads wear out. Just replace the pads, and bed in the new pads properly.

Here is a great read from StopTech on brakes.

 

Rotors are relatively cheap, so be good to your car and never, ever turn rotors!

Treat your brakes like BMW brakes, when the rotors need help, just replace...