Section 44A. 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 janitor whose employment began before July first, nineteen hundred and thirty-seven, and 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, or who has completed a service of not less than fifteen years and is physically or mentally incapacitated for labor by reasons of injury received in the performance of his duties for such city or town; and if so retired his pension shall be equal to seventy-two per cent of the annual rate of compensation payable to such employee on the date of his retirement and shall be payable out of the appropriation for the support of public schools, maintenance of school buildings or payment of janitors.