Persons who become members of the fire department after the eighth day of January, 1932 and prior to July 1, 1949, shall become members of the Retirement System subject only to the following provision in addition to the provisions contained in Sections 3.670-3.672, 8.500-8.502, 8.510, 8.511, 8.520, 8.525 and 8.560 of this Charter. No member of the Retirement System shall be retired, except in case of disability incapacitating him for the performance of his duties, unless he shall have attained the age of 55 years and completed 20 years of continuous service, except that retirement shall be compulsory at the age of 70 years. It may be provided, however, under such Retirement System, that members may retire after 30 years of continuous service; the benefits at retirement in such cases to be determined, because of retirement at an age below 55, in accordance with the tables recommended by the actuary and approved by said retirement board.