“Which of you by taking thought can add one cubit unto his stature?”
King James Version (KJV)
6:27 And which of you - If you are ever so careful, can even add a moment to your own life thereby? This seems to be far the most easy and natural sense of the words.
Mt 6:27 Which of you by being anxious, etc. There can hardly be a doubt that this ought to be rendered, "add one cubit to his age", or period of life. The idea is: "What is the use of anxiety? Who, by his anxiety, can add anything to life's journey"? If it is proper to speak of "'length' of life", it is also appropriate to speaking of adding a cubit to its length.