Psalm 61:6:

Thou wilt prolong the king’s life: and his years as many generations.

Notes on Psalm 61:6:

David expected long life.  How long a life did he expect?  He said “many generations.”  I don't know how young they were when they had kids back then, but I suppose that “many generations” would be 70 years in David’s time.  (This could be about 4 generations.)  I suppose that because David was 30 years old when he became king, and he reigned for 40 years, which would make him 70 years old when he died.  That was probably well beyond the life expectancy of the time, although Elisha lived substantially longer.  70 to 80 years was a sign of BAD TIMES in Israel based on Psalm 90:10, and David certainly lived through some tumultuous times.  I don’t know how short David’s life would have been if God hadn’t extended it.

The fact that God prolongs life indicates that you should live longer knowing God than you would have lived without knowing Him.