“It is never too late to reform, as long as you have the sense to desire it, and the strength to execute your purpose.”

Preface xxx
Variant: When philosophy paints its grey on grey, then has a shape of life grown old. By philosophy's grey on grey it cannot be rejuvenated but only understood. The owl of Minerva spreads its wings only with the falling of the dusk.
As translated by T. M. Knox, (1952) <!-- p. 13 -->
Elements of the Philosophy of Right (1820/1821)
Context: Only one word more concerning the desire to teach the world what it ought to be. For such a purpose philosophy at least always comes too late. Philosophy, as the thought of the world, does not appear until reality has completed its formative process, and made itself ready. History thus corroborates the teaching of the conception that only in the maturity of reality does the ideal appear as counterpart to the real, apprehends the real world in its substance, and shapes it into an intellectual kingdom. When philosophy paints its grey in grey, one form of life has become old, and by means of grey it cannot be rejuvenated, but only known. The owl of Minerva takes its flight only when the shades of night are gathering.

Source: The Curious Case of Benjamin Button Screenplay

Source: Life, the Truth, and Being Free (2010), p. 46

2022, June 2022, Remarks by Vice President Harris Announcing the Launch of the White House Task Force to Address Online Harassment and Abuse

The Book of Delusions (1936)

Variant: One of the great secrets of life. Most people die of a sort of creeping common sense and discover too late that the only things one never regrets are one's mistakes.
Source: The Picture of Dorian Gray

Source: And the Mountains Echoed