Provided are methods of aging an x-ray generator having carbon nanotube electron emitters. The method of aging an x-ray generator that includes a cathode, a gate electrode, and an anode, includes applying a desired, or alternatively predetermined anode voltage to the anode, and applying a direct current pulse voltage to the gate electrodes to emit electrons from electron emitters. The method further includes maintaining an anode current formed by electrons generated from the electron emitters constant.