Brake Pulsation - Warped Rotors

I have an 05 Saturn Relay with 47000 miles and I am getting the normal "disks are warped" pulsation when applying the brakes. I have front and rear disks, so how do I determine which disks need replacing? There is not much pulse in the steering wheel, which makes me think it is the rears. But at 47000 miles, how can I need rear brakes already? Are there issues with calipers?

Any help would be appreciated.

Thanks

The rotors warping have nothing to due with the brakes being worn out.

If you feel it at all in the steering wheel that it is the fronts. If you feel it more in the seat it is the rears. The rears have to be really bad for you to feel them so more often than not its usually the fronts that are causing the pulsation.

Improper wheel torque, improper installation, debris between the rotor and hub, hot spots, and rust spots across the rotors surface can all contribute to a rotor warping.

The cause of pulsation and vibration are warped brake rotors. When applying the brakes, press brake calipers brake pads against the rotors that rotate with the wheel. If the rotor is warped at the surface are not parallel, the pistons are quickly pushed in and out of contact pads highs and lows.