Section 58D. In any city or town which accepts this section, if any city or town employee, other than a member of the police department or a permanent member of the fire department, who is a veteran, retires under section fifty-eight, he shall, in lieu of the retirement allowance provided in said section fifty-eight, receive a retirement allowance, if he retires before attaining age sixty, equal to seventy per cent, after attaining age sixty and before attaining age sixty-one, equal to seventy-one per cent, or after attaining age sixty-one, equal to seventy-two per cent, of the highest annual rate of compensation, including any bonuses paid in lieu of additional salary or as a temporary wage increase in addition to his regular compensation, and including any maintenance allowance, payable to him while he was holding the grade held by him at his retirement, and payable from the same source.