1. All judges other than municipal judges shall retire at the age of seventy years, except as provided in the schedule to this Article, under a retirement plan provided by law.

2. All judges may retire at an earlier age authorized by law and may participate in a retirement plan provided by law.

3. Any retired judge, associate circuit judge or commissioner, with his consent, may be assigned by the supreme court as a senior judge to any court in this state or as a special commissioner. When serving as a senior judge he shall have the same powers as an active judge.