Midrasch zu Schemuel II 19:35

And God almighty give you mercy before the man (Gen. 43:14). Scripture states elsewhere in allusion to this verse: For this let everyone that is godly pray unto Thee in a time when Thou mayest be found (Ps. 32:6). R. Abba maintained: In a time when Thou mayest be found refers to old age. It is essential that a man pray for an old age in which his eyes may see, his mouth may eat, and his feet may walk. Normally, when a man becomes old, his faculties leave him. For example, it is written about Isaac: And it came to pass, that when Isaac was old, and his eyes were dim, so that he could not see (Gen. 27:1). And concerning Jacob, Scripture states: Now the eyes of Israel were dim for age, so that he could not see (Gen. 48:10). As to a mouth that could not eat, we find that Barzillai said to David: Can thy servant taste what I eat or what I drink? Can I hear anymore the voice of singing men and singing women? Therefore, then, should thy servant be a burden unto my lord the king? (II Sam. 19:35).