'Eighty' in the Bible

and Barzillai is very aged, a son of eighty years, and he hath sustained the king in his abiding in Mahanaim, for he is a very great man;

A son of eighty years I am to-day; do I know between good and evil? doth thy servant taste that which I am eating, and that which I drink? do I hearken any more to the voice of singers and songstresses? and why is thy servant any more for a burden unto my lord the king?