What do mankinds greatest and worst generations have to do with one another?
“The Fountain of Youth” … why has mankind been searching for it from time immemorial?
And HaShem said: “My Spirit shall not keep on judging man forever, for he is nothing but flesh. His days will be a hundred and twenty years.â€
— Bereshis 6:3
I will be slow to anger for 120 years. If they do not repent I will bring the Flood upon them.
— Rashi ibid
Where is Moshe alluded to in the Torah? — In the verse: “For he is nothing but flesh†[the gimatriya-numerical value; of the Hebrew words משה –“Moshe†and ×‘×©×’× Â – “For (he) is nothing but†are equivalent. Moshe lived exactly 120 years]
— Chulin 139BR
Go [My prophet] and call into the ears of Jerusalem, declaring: HaShem says as follows: For you[r sake] I will remember the affection of your youth, the love of your nuptials; how you followed Me into the wilderness, into an uncultivated land.
— Yirmiyahu 2:2
Remember, HaShem, Your compassion and Your loving-kindnesses; for they began before time. Do not remember the sins of my youth, nor my transgressions …
— Tehillim 25:6,7
Who Satiates your old age with good; so that your youth will be renewed like the eagle.
— Tehillim 103:5
Youth is an uncanny time in our lives. While imprisoned within it we want nothing more than to escape it. Once we have escaped it we spend the balance of our lives yearning wistfully and futilely to return to it. By turns we long for the carefree times, irresponsibility, limitless possibilities, direction-changing impressions, dependence
on-others, physical attractiveness, good health, idealism and the simplicity of time when we were young.  From ancient and 16th century legends of Ponce de León searching for the Fountain of Youth to the contemporary multibillion dollar cosmetics and cosmetic surgery industries; vast swaths of mankind have never ceased looking for ways and means of recapturing youth.
Most of all we long for the sheer vitality, power and strength that marks our early lives. When we were young we had the speed, strength, stamina, mental acuity, inquisitiveness, reckless courage and optimism to accomplish great and meaningful things. Many used their youthful, robust powers for good. However, lacking the skill and wisdom of age and experience; youth is also characterized by catastrophic mistakes, crimes and misdemeanors. Accelerating at youthful takeoff velocity, the young often take forks in life’s road that make U-turns impossible. The lion’s share of crimes is committed by the young.  Maturity and old-age are marked not only by longing for the restoration of youthful energy, but by remorse and regret over youthful indiscretions and catastrophic misdeeds.
Rav Tzadok, the Kohen of Lublin, teaches that this is not merely true of individuals but for mankind as a whole. In its youth mankind was capable of great virtue and good — chessed neurim-the lovingkindness of youth; and of incredible transgression and evil — chatas neurim-the sins of youth.