40 ILCS 5/6-138

Widow's annuity shall be computed as herein provided, except that the maximum age of the widow for annuity purposes for the wife or widow of any employee entering service prior to July 1, 1953, shall not be more than 5 years less than the age of the employee as of the date when such wife's or widow's annuity is fixed; and for the widow of a future entrant entering service after June 30, 1953, her maximum age for annuity purposes shall in no event be more than the age of her husband as of the date when such wife's or widow's annuity is fixed.