Section 36A. Any town which has not accepted chapter four hundred and eighty-seven of the acts of nineteen hundred and thirteen and shall accept this section by vote of the town at a town meeting, and has a call or part call fire force which now is or may hereafter be subject to chapter thirty-one, may, on the recommendation of the appointing officer of the fire department, promote to membership in the regular or permanent full-time force, without civil service examination and without any probationary period of service required under said chapter thirty-one and the rules made thereunder, any persons then in the call or part call fire force who have served as call men or part call men or substitute call men for three or more successive years, and who are certified to be competent physically for the duty by the town physician, if any, otherwise by a physician designated therefor by said appointing officer. Appointments from the call force to the regular or permanent force shall be made by the appointing officer upon certification by the personnel administrator from the list of members of the call force of firemen, in accordance with the rules of the civil service commission, except that the basis of certification shall be the order of appointment to the call force, or, if not ascertainable, the order of the respective ratings of such members obtained in the examination upon which the list of eligibles for appointment to such call force was based. No person who has passed his fiftieth birthday shall be appointed from such a call force to such a regular or permanent force.