(a) The Chief Justice or any associate justice of the Supreme Court, any judge of the Court of Civil Appeals or any judge of the Court of Criminal Appeals serving on September 18, 1973, who elects to become a member of the retirement system hereby established, and any such justice or judge assuming such office after September 18, 1973, may elect to be retired pursuant to this article if he:
(1) Has served as much as five years as a justice of the Supreme Court or as a judge of one of the courts of appeals or as a judge of the circuit court or any two or more of them consecutively and has become permanently physically or mentally unable to carry out his duties on a full-time basis, proof of such disability being made by certificate of three reputable physicians;
(2) Has served for 12 years as a justice of the Supreme Court or as a judge of one of the courts of appeals or one of the circuit courts or any two or more of them and has reached or passed the age of 65 years;
(3) Has served for 15 years as a justice of the Supreme Court or as a judge of one of the courts of appeals or one of the circuit courts or any two or more of them and has attained age 62 less one year for each year of service in excess of 15;
(4) Has served for 10 years as justice of the Supreme Court or as a judge of one of the courts of appeals or one of the circuit courts or any two or more of them and is not less than 70 years of age; or
(5) Has served for not less than 18 years or three full terms or a time equal to three full terms as a justice of the Supreme Court or as a judge of one of the courts of appeals or one of the circuit courts.
(b) Any judge of a circuit court who was serving on September 18, 1973, who elects to become a member of the retirement fund hereby established and any circuit judge assuming such office after September 18, 1973, may elect to be retired pursuant to this article if he:
(1) Has served as much as five years as a circuit judge and has become permanently physically or mentally unable to carry out his duties on a full-time basis, proof of such disability being made by certificate of three reputable physicians;
(2) Has served for 12 years as a circuit judge and has reached or passed the age of 65 years;
(3) Has served for 15 years as circuit judge and is not less than 62 years of age or has served as such for more than 15 years and has attained age 62 less one year for each year of service in excess of 15;
(4) Has served continuously for 10 years as circuit judge and is not less than 70 years of age; or
(5) Has served for not less than 18 years or three full terms or a time equal to three full terms as a circuit judge.