The board of trustees is authorized to adopt a method of providing postretirement benefit adjustments for a beneficiary in his postretirement years. Such method of adjustment may result in the adoption by the board of trustees of a method of financing other than that described in paragraphs (1) through (3) of Code Section 47-3-43 and shall be based upon:

(1) Recommendation of the actuaries for the board of trustees; and

(2) Maintaining the actuarial soundness of the system.

The board of trustees may specify a minimum age which a beneficiary must have attained in order to be eligible for the postretirement benefit adjustment.