Xjyuk

וַיִּגְדַּל הַיֶּלֶד וַיִּגָּמַל וַיַּעַשׂ אַבְרָהָם מִשְׁתֶּה גָדוֹל בְּיוֹם הִגָּמֵל אֶת־יִצְחָק׃

The child [Itzchak] grew up and was weaned, and Abraham held a great feast on the day that Isaac was weaned. (Rashi/B"R - 24 months) Ber. 21,8

Usually, we turn all of our forefather's behaviors into traditions even when they weren't commanded. But I don't recall throwing such a Seudah for my kids, neither participating in those of others'.

The Torah does not repeat that tradition for other descendants, but neither it mentions having circumcision, so we don't have a "one-time" claim.

Why this custom didn't make it into our tradition?

According to one opinion in the Midrash (Bereishis Rabbah 53:10), we do.

וַיִּגְדַּל הַיֶּלֶד וַיִּגָּמַל (בראשית כא, ח), רַבִּי הוֹשַׁעְיָה רַבָּה אָמַר נִגְמַל מִיֵּצֶר הָרָע. רַבָּנָן אָמְרֵי נִגְמַל מֵחֲלָבוֹ.

”And the child grew up and was weaned” – R’ Hoshaya Rabbah said, “He was weaned from the evil inclination.” The Rabbis say, “He was weaned from his milk.

As Etz Yosef ad. loc. explains R’ Hoshaya’s opinion:

נגמל מיצר הרע פירוש שנעשה בן י"ג שנה שאז נגמל הנער מיצה"ר שהוא כח התאווה החומרית ונכנס בו כח היצר טוב. ולכן מאז הוא מצווה ועושה. ולשמחה זו עשה אברהם משתה:

”He was weaned from the evil inclination” – the explanation is that he became a 13-year-old, that then the lad was weaned from his evil inclination, which is the power of strong desire, and the good inclination entered into him. Therefore, from then he was “one who was commanded and does,” and for this joy Avraham made a feast.

As Chabad notes, while the Bar Mitzvah celebration is a fairly recent custom, some 400 years old, this Midrash seems to be a strong source for doing so.

I once heard (do not remember from who) that this Seuda was to thank Hashem for the major miracle that happened to Sara who was 90 when she gave birth to Yitzchok. She has already gone through menopause and the miracle of giving birth and then being able to nurse was major.

Perhaps as we do not merit such a miracle, woman do not have children once they are that stage, therefore we do not make such a Seuda.

Rashi states explicitly to Bereshit 21:8 that this was af the completion of the first 24 months of Yitzchok's life and as the Ikar Siftei Chachamim states, it coincided with Yitzchok no longer breast feeding from his mother, Sarah. Yitzchok began to consume wheat flour which is compared to Torah by Rabbi Elazar ben Azaryah like is found in Avot 3:17.

רַבִּי אֶלְעָזָר בֶּן עֲזַרְיָה אוֹמֵר, אִם אֵין תּוֹרָה, אֵין דֶּרֶךְ אֶרֶץ. אִם אֵין דֶּרֶךְ אֶרֶץ, אֵין תּוֹרָה. אִם אֵין חָכְמָה, אֵין יִרְאָה. אִם אֵין יִרְאָה, אֵין חָכְמָה. אִם אֵין בִּינָה, אֵין דַּעַת. אִם אֵין דַּעַת, אֵין בִּינָה. אִם אֵין קֶמַח, אֵין תּוֹרָה. אִם אֵין תּוֹרָה, אֵין קֶמַח.

So if you're looking for what celebration we actually do today that is associated with this, it would be the Upsherin, the first haircut given to a young Jewish boy after they enter their third year of life or as late as the completion of their 3rd birthday. At that time, the boy begins his formal Torah education and starts wearing tzitzit. See this Wikipedia page discussing the practice of Upsherin.

The difference in the two time ranges is to coincide with completing the 24 months like with Avraham, Sarah and Yitzchok, their son and the prohibition of Orlah, not benefitting from the fruit of Eretz Yisrael for the first 3 years.

Upsherin is practiced by many different Chassidic branches, Kabbalists following the teachings of the Ari z"l, and as noted in נטעי גבריאל - תגלחת הילדים הולכתם לחדר וסעודת החומש, Chapter 2, page 35, footnote 2, this is also the practice of some of the Jews of Yemen.