'Old' in the Bible

"How is it possible," Nicodemus asked, "for a man to be born when he is old? Can he a second time enter his mother's womb and be born?"

"You are not yet fifty years old," cried the Jews, "and have you seen Abraham?"

"In most solemn truth I tell you that whereas, when you were young, you used to put on your girdle and walk whichever way you chose, when you have grown old you will stretch out your arms and some one else will put a girdle round you and carry you where you have no wish to go."