A member of the police department may retire for service pursuant to this section. Upon receipt of a member’s application for retirement, the board shall order him retired from further service. From the date of the order the service of the member in the police department ceases and during his lifetime he shall be paid from the fund an annual pension based upon the following schedule:
(a)
If he has attained age 60 and served in the police department for twenty years, or more, in the aggregate, his annual pension shall be one-half of the annual salary attached to the rank he held for one year next preceding retirement.
(b)
If he has attained age 60 and has served in the police department for thirty years, or more, in the aggregate, his annual pension shall be two-thirds of the annual salary attached to the rank he held for one year next preceding retirement.
(c)
If he has attained age 55 and has served in the police department for twenty-five or more consecutive years, his annual pension shall be one-half of the annual salary attached to the rank he held for one year next preceding retirement.