horae quidem cedunt et dies et menses et anni, nec praeteritum tempus umquam revertitur nec quid sequatur sciri potest. quod cuique temporis ad vivendum datur, eo debet esse contentus.Cicero, On Old Age, 19.69. My translation.
Hours, days, months and years pass by, the past never returns, and the future cannot be known: but we should be content with whatever time we are given to live within.