Chasidut for Pirkei Avot 5:21
הוּא הָיָה אוֹמֵר, בֶּן חָמֵשׁ שָׁנִים לַמִּקְרָא, בֶּן עֶשֶׂר לַמִּשְׁנָה, בֶּן שְׁלשׁ עֶשְׂרֵה לַמִּצְוֹת, בֶּן חֲמֵשׁ עֶשְׂרֵה לַתַּלְמוּד, בֶּן שְׁמֹנֶה עֶשְׂרֵה לַחֻפָּה, בֶּן עֶשְׂרִים לִרְדֹּף, בֶּן שְׁלשִׁים לַכֹּחַ, בֶּן אַרְבָּעִים לַבִּינָה, בֶּן חֲמִשִּׁים לָעֵצָה, בֶּן שִׁשִּׁים לַזִּקְנָה, בֶּן שִׁבְעִים לַשֵּׂיבָה, בֶּן שְׁמֹנִים לַגְּבוּרָה, בֶּן תִּשְׁעִים לָשׁוּחַ, בֶּן מֵאָה כְּאִלּוּ מֵת וְעָבַר וּבָטֵל מִן הָעוֹלָם:
He was wont to say: Five years old for (learning) Scripture. [This is derived from arlah (forbidden fruit), viz. (Leviticus 19:23): "Three years shall it be forbidden to you… (24): And in the fourth year all of the fruit shall be holy for praise to the L rd." (At this stage) his father teaches him the form of the letters and the vowel signs. (25): "And in the fifth year you may eat its fruit, to increase for you its produce." Thenceforward, stuff him like an ox!], ten years old for Mishnah. [He learns Scripture for five years and Mishnah for five years, viz. (Chullin 24a): The master said: Any student who has not made progress in his Mishnah after five years, will no longer do so, as it is written (Numbers 8:24): "This is what applies to the Levites. From the age of twenty-five and up shall he come to enter into service to work in the tent of meeting." He learns the halachoth of the service for five years, and, at thirty, he works.], thirteen years old for mitzvoth, [it being written (Numbers 5:6): "A man or a woman if they do of all the sins of man" and, in respect to (the episode of ) Shchem, (Genesis 34:25): "And two sons of Jacob, Shimon and Levi, the brothers of Dinah, took, each man his sword, etc." Levi at that time was thirteen years old and he is called "a man"], eighteen for the (marriage) canopy. ["Adam" ("man") is written nineteen times in the parshah of Bershith — from (1:26): "And G-d said: "Let us make a man" until (2:22): "And the L rd G-d fashioned the side that He had taken from the man into a woman" — one time for (the plain meaning) itself, leaving eighteen for expounding ("derashah").], twenty years old for pursuing [a livelihood. After he has learned Scripture, Mishnah, and Gemara, and taken a wife and begotten children, he must pursue a livelihood. Or: "twenty years old for pursuing" him from Heaven and punishing him for his acts, the Heavenly tribunal not punishing one who is less than twenty years old.], thirty for strength, [the Levites setting up the tabernacle and taking it apart and loading the wagons and carrying on their shoulder from the age of thirty on], forty years old for understanding, [for after forty years that Israel was in the desert Moses said to them (Deuteronomy 29:3): "and the L rd did not give you a heart to know and eyes to see and ears to hear until this day."], fifty years old for counsel, [it being stated of the Levites (Numbers 8:25-26): "And from the age of fifty he shall return from the service of the work, and he shall serve no more. And he shall serve his brothers." Which service? Counsel.], sixty years old for old age, viz. (Iyyov 5:26): "You will go to the grave in old age (bekelach): — the gematria (numerical equivalent) of "bekalach" is sixty.], seventy years old for hoary old age, [it being written in respect to David (I Chronicles 29:28): "And he died in a good hoary old age, and the days of his life were seventy years."], eighty years old for strength, [it being written (Psalms 90:10): "And if with 'strengths,' eighty years."], ninety years old for bowing (shuach) [He walks bowed and bent over. Some see it as relating to "shuchah amukah," "a deep pit."], one hundred years old — as if he had died and passed on and vanished from the world.