(2) from his sixty-fifth birthday, monthly benefits for life equal to the difference between(a) the monthly benefits to which he is entitled, at the date of the option, under the Workers’ Compensation Act; and
(b) the amount obtained by dividing the amount contemplated in paragraph 1, less the amount contemplated in subparagraph a, by the factor, less the number one, provided for in Schedule VIII according to his age at the date of the option.