Upon death of an employee or annuitant occurring on or after January 1, 1976, who has completed at least 20 years of service and has established accumulations for such annuity by employee contributions as provided in Section 12-151 hereof, plus the prescribed concurrent contributions by the employer, the annuity to the surviving spouse shall in no event be less than one-half of the retirement annuity which had accrued to an employee if death occurs while in service, or one-half of the amount of retirement annuity of the retired employee on the date of death; provided that if the age of the surviving spouse is less than 60 years at the date of death of the employee or annuitant, the annuity to the spouse shall be reduced 1/2 of 1% for each month that such age is less than 60 years.
     If the minimum annuity survivor’s benefit provided in this Section exceeds the maximum survivor’s benefit payable under Section 12-125 or 12-135, such minimum benefit shall be payable.