The Governor and lieutenant governor must be citizens of the United States, have attained the age of twenty-one years, and be residents of the State of South Dakota for two years preceding their election. They shall be jointly elected for a term of four years at a general election held in a nonpresidential election year. The candidates having the highest number of votes cast jointly for them shall be elected. Commencing with the 1974 general election, no person shall be elected to more than two consecutive terms as Governor or as lieutenant governor. The election procedure shall be as prescribed by law.