Psalms 102:23

And this is true. For no one is able to comprehend the works of God altogether. Moreover, the world is the work of God. No one, then, can find out as to this world what is its space from the beginning and to the end, that is to say, the period appointed for it and the limits before determined for it; in view of the fact that God has set the whole world as a realm of ignorance in our hearts. And thus one says, "Declare to me the shortness of my days." In this manner, and for our profit, the end of this world [age]—that is to say, this present life—is a thing of which we are ignorant.

Now as these things are written in the Scriptures, the case is clear, that the saints know that a certain time is measured to every person, but that no one knows the end of that time is plainly intimated by the words of David, "Declare to me the shortness of my days." He desired information about that which he did not know. Accordingly the rich man also, while he thought that he had still a long time to live, heard the words, "You fool! This very night your life will be demanded from you. Then who will get what you have prepared for yourself?" And the Preacher speaks confidently in the Holy Spirit and says, "A person also does not know his time." Wherefore the patriarch Isaac said to his son Esau, "Behold, I am old, and I know not the day of my death."

For although it is hidden and unknown to all, what period of time is allotted to each and how it is allotted, yet every one knows this, that as there is a time for spring and for summer, and for autumn and for winter, so, as it is written, there is a time to die and a time to live. And so the time of the generation that lived in the days of Noah was cut short, and their years were contracted, because the time of all things was at hand. But to Hezekiah were added fifteen years. As God promises to them that serve him truly, "I will fulfill the number of your days," Abraham dies "full of days," and David urgently begged God, saying, "Don't take me away in the midst of my days." And Eliphaz, one of the friends of Job, being assured of this truth, said, "You shall come to your grave like ripe corn, gathered in due time, and like as a shock of corn comes in its season." Solomon, confirming his words, says, "The souls of the unrighteous are untimely taken away." And therefore he exhorts in the book of Ecclesiastes, saying, "Don't be too wicked, neither be hard: why should you die before your time?"