Be it further enacted, That all bonds issued under this Act may be made callable on any interest maturity date occurring five (5) years or more after date of issuance, and for such purpose a premium may be paid. Bonds called shall be called in inverse order according to maturity, so that the bonds having the longest maturity shall be called first. Provisions of the callable feature shall be set out in the bond ordinance and shall appear likewise on the face of each callable bond.