This quote was taken by a 2,000-year-old philosophical work by Seneca, ‘On The Shortness of Life’. Long before there were Napoleon Hill, Anthony Robbins, or any other speakers alike, and so long before human life expectancy was dramatically improving like now this century (which could also be one defining factor), the Roman philosopher had offered us timeless advice (and also a cautious warning) on how to make the best use of our time as long as we are still alive in this world:
You are living as if destined to live for ever; your own frailty never occurs to you; you don’t notice how much time has already passed, but squander it as though you had a full and overflowing supply — though all the while that very day which you are devoting to somebody or something may be your last. You act like mortals in all that you fear, and like immortals in all that you desire… How late it is to begin really to live just when life must end! How stupid to forget our mortality, and put off sensible plans to our fiftieth and sixtieth years, aiming to begin life from a point at which few have arrived!
Read more about his work in Brain Pickings.