(1) A class A member shall have attained sixty-five (65) years of age;
(2) A class B member shall have attained sixty (60) years of age, and have twenty (20) years of creditable service, or shall have thirty (30) years of creditable service without regard to age;
(3) A class C member shall have attained fifty (50) years of age and shall have twenty-five (25) years of creditable service, or shall have thirty (30) years of creditable service without regard to age.