Complex sentence: He served as 29th Governor of South Dakota from 1993 to 1995, having assumed the duties of the governorship upon the death of George S. Mickelson, and, at age 67, the oldest person to serve as Governor of South Dakota.
Split into simpler sentences: He served as 29th Governor of South Dakota from 1993 to 1995, having assumed the duties of the governorship upon the death of George S. Mickelson. He was, at age 67, the oldest person to serve as Governor of South Dakota.