This section does not apply to ordinary policies issued on or after the operative date of section 26.1-33-24. In the case of ordinary policies issued on or after the operative date of this section, all adjusted premiums and present values referred to in sections 26.1-33-18 through    26.1-33-28 must be calculated on the basis of the commissioners 1958 standard ordinary mortality table and the rate of interest specified in the policy for calculating cash surrender values and paid-up nonforfeiture benefits, provided that the rate of interest may not exceed three and one-half percent per annum except that a rate of interest not exceeding five and one-half percent per year may be used for policies issued after June 30, 1977, except that for any single premium whole life or endowment insurance policy a rate of interest not exceeding six and one-half percent per year may be used; and provided that for any category of ordinary insurance issued on female risks, adjusted premiums and present values may be calculated according to an age not more than six years younger than the actual age of the insured. In calculating the present value of any paid-up term insurance with accompanying pure endowment, if any, offered as a nonforfeiture benefit, the rates of mortality assumed may be not more than those shown in the commissioners 1958 extended term insurance table. For insurance issued on a substandard basis, the calculation of any such adjusted premiums and present values may be based on such other table of mortality as may be specified by the insurer and approved by the commissioner. Upon the operative date of this section, any insurer may file with the commissioner a written notice of its election to comply with the provisions of this section after a specified date before January 1, 1966. After the filing of such notice, upon the specified date, which must be the operative date of this section for that insurer, this section becomes operative with respect to the ordinary policies issued by the insurer after that date. If an insurer makes no election, the operative date of this section for the insurer is January 1, 1966.