Complex sentence: David O. McKay was called to the presidency of the LDS Church in 1951, when he was 78 years old, and he served for 19 years as prophet and president before his death in 1970.
Split into simpler sentences: David O. McKay was called to the presidency of the LDS Church in 1951, when he was 78 years old. He served for 19 years as prophet and president before his death in 1970.