Section 77D. A city having a plan D or plan E charter by a two thirds vote of all the members of its city council, any other city by a vote of the city council subject to the provisions of its charter and a town by a majority vote at an annual town meeting may direct the appropriate city or town retirement board to retire, at his own request, any laborer who has been in such employ for not less than thirty-five years, or who has reached the age of sixty and has been in such employ for not less than twenty-five years and has become physically or mentally incapacitated for labor, and any laborer in the employ of such city or town who has been in such employ for not less than fifteen years and has become physically or mentally incapacitated for labor by reason of any injury received in the performance of his duties for such city or town; and if so retired he shall receive from the city or town for the remainder of his life an annual pension equal to seventy-two per cent of his annual rate of regular compensation for full time service as a laborer at his retirement.