Min. rotor thickness should be stamped on the "hat" of each rotor. You have not said if the rotors on there are original or had been replaced with aftermarket, so I cannot say what the Min. thickness is. Rotors every other pad change is generally true, especially up front. Rears may go every thrid pad change, depending on the loading of the vehicle. This is assuming standard semi-metalic pads.

If you want them (rotors) to last longer, go with basic ceramic pads (like the ones from Satisfied). Same stopping distance and power, but quiter, much easier on rotors, and best of all, leave your wheels cleaner than you can imagine.