The following teaching appears toward the end of the fifth chapter of the Vilna Edition of Tractate Avoth:
הוּא הָיָה אוֹמֵר: בֶּן חָמֵשׁ שָׁנִים לְמִקְרָא, בֶּן עֶֽשֶׂר שָׁנִים לְמִשְׁנָה, בֶּן שְׁלֹשׁ עֶשְׂרֵה לְמִצְוֹת, בֶּן חֲמֵשׁ עֶשְׂרֵה לִגְמָרָא, בֶּן שְׁמוֹנֶה עֶשְׂרֵה לְחֻפָּה, בֶּן עֶשְׂרִים לִרְדּוֹף, בֶּן שְׁלֹשִׁים לְכֹֽחַ, בֶּן אַרְבָּעִים לְבִינָה, בֶּן חֲמִשִּׁים לְעֵצָה, בֶּן שִׁשִּׁים לְזִקְנָה, בֶּן שִׁבְעִים לְשֵׂיבָה, בֶּן שְׁמוֹנִים לִגְבוּרָה, בֶּן תִּשְׁעִים לָשֽׁוּחַ, בֶּן מֵאָה כְּאִלּוּ מֵת וְעָבַר וּבָטֵל מִן הָעוֹלָם.
He would also say: Five years old for [the study of] Scripture. Ten years old [for the study of] Mishna. Thirteen years old for [the obligation to keep] the commandments. Fifteen years old for Talmud [study]. Eighteen years old, for marriage. Twenty years old, to pursue [a living]. Thirty years old, for strength. Forty years old, for understanding. Fifty years old, for counsel. Sixty years old, for sagacity. Seventy years old, for elderliness. Eighty years old, for strength. Ninety years old, to stoop. A hundred years old, is as though one has died and passed, away and no loger of this world.
Interestingly enough, Maimonides’s version of the mishna does not include this classic teaching, and I guess there are other manuscripts (https://cudl.lib.cam.ac.uk/view/MS-ADD-00470-00001/299) that also do not have it. But, many of its ideas can be found elsewhere in the teachings of the sages, e.g., in Avoda Zara 5b:
אף משה רבינו לא רמזה להן לישראל אלא לאחר ארבעים שנה שנאמר (דברים כט) ואולך אתכם במדבר ארבעים שנה וכתיב (דברים כט) ולא נתן ה’ לכם לב וגו’ אמר רבה ש”מ לא קאי איניש אדעתיה דרביה עד ארבעין שנין
Even Moses only hinted at this to the Israelites after forty years had passed, as it is said, “I led you forty years in the wilderness.. but the Lord has only this day given you a heart to know, eyes to see, and ears to hear.” Rabba said: “From this you can learn that one only comprehends his master’s opinion after forty years.
Only after being guided by Moses for a full forty years could the people begin to understand things from his perspective.
Earlier, we saw how David led an ideological revolution. When he first became king, he was the only one who was practically trying to build the Temple, but as his forty year reign was coming to an end, the people saw him as an impediment, that he was the one who was now preventing them from building the Temple. I once thought that Moses’s and David’s achievements were in that they were able to change people’s perceptions and goals, but in both cases, they were actually addressing different generations. The original generation that Moses led was condemned to pass away before achieving their ultimate goal, while the Talmud describes how men in David’s generation would fall in battle because they did not properly seek the building of the Temple. The ones whom Moses addressed at the end of his ministry and the ones who could not wait for Solomon’s ascension were the youngsters, the ones Moses and David had raised, new, uncorrupted generations that had grown up free and proud and idealistic, and without the mentality of the oppressed. 22 years ago, when I first came to Israel, barely any Jews ascended the Temple Mount, and absolutely no one was allowed to pray there, but now, although there is still so much more for us to do, public Jewish prayers are conducted there many times each day. Ten years ago, I had to sneak onto the Temple Mount disguised as a gentile in order to pray there on the Ninth of Av, while this past year, hundreds of Jews gathered on the Temple Mount on the Ninth of Av, and it was clear that the average age of the assembled was not much more than twenty. Indeed, a few years ago, Rabbi David Avihail told me that the ever-increasing rate of Jewish Pilgrimage to the Temple, despite the rabbinic establishment’s opposition thereto (an establishment of which he was a part of), was a positive example of what the Kabbalists term an “awakening from below,” that would lead to the rebuilding of the Temple.
I thank God for bringing me to this milestone, for allowing my children to visit His house before they even reached “the age of mitzwoth,” and it is my sincere prayer that the coming years herald even greater advancements for our people.
Avraham Ben Yehuda 