1999 Other Oldsmobile Models Rotors

Replace them when you replace the pads. I would expect 25-35,000 miles. Turning/maching them will almost always result in a pulsation. I assume we are talking fronts.
Things that help are keeping the rear brakes adjusted and not hard stopping and amount of city driving. Letting them set too long will cause them to deteriorate in the form of pitting. Improper replacement of pads or other weak braking components can have an affect as well.