Elective officials who are eligible to receive retirement benefits in accordance with the provisions hereinabove stated shall receive and be paid a monthly retirement allowance as follows:
(1) Those who have completed at least twenty years but less than thirty years of creditable service shall receive and be paid a monthly allowance equal to fifty percent of one-twelfth of the annual salary received by him during the twelve month period immediately preceding the date of his retirement.
(2) Those who have completed thirty or more years of creditable service shall receive and be paid a monthly allowance equal to sixty-five percent of one-twelfth of the annual salary being received by him at the time of his application for retirement.