If any judge of probate is separated after January 1, 1972, from the service of his court after having completed ten years of credited service as judge of probate, he may elect to take a retirement allowance to commence on the first day of any month following the date of separation. The allowance shall be payable in an amount determined by the Retirement Commission to be the actuarial equivalent of the retirement allowance that would have been payable except for the election of such option, except that for any such judge separated on or after October 1, 1986, who has attained the age of sixty, the reduction of the allowance which would have been payable shall be one-quarter of one per cent for each month his retirement precedes his attainment of age sixty-two. Any such judge of probate, who was separated from the service of his court before July 1, 1979, with at least ten years but less than twelve years of credited service may elect a retirement allowance retroactive to January 1, 1979, or the first day of the month after such separation, whichever is later.