Was Rebecca 3 when she a married a 40 years old Isaac ?

According to Rashi . Rebecca was 3 when she married 40 years old Isaac

Here a quote from Rashi , the greatest Rabbi , Sage in Judaism about Genesis

בן ארבעים שנה

FORTY YEARS OLD — For when Abraham came from Mount Moriah he received the news that Rebecca was born (22:20). Isaac was then thirty-seven years old, because at that time Sarah died and from the birth of Isaac until the Binding — when Sarah died — there were 37 years since she was 90 years old when Isaac was born and 127 when she died, as it is said, (23:1) “And the life of Sarah was [one hundred and twenty seven years]” — thus Isaac was then 37 years old. At that period Rebecca was born and he waited until she was fit for marriage — 3 years — and then married her (Seder Olam).

➡️➡️➡️

Maimonides agrreed with the age of three

10.. If, by contrast, a Jewish male enters into relations with a gentile woman, when he does so intentionally, she should be executed.23 She is executed because she caused a Jew to be involved in an unseemly transgression, as is the law with regard to an animal.24 This applies regardless of whether the gentile women was a minor of three years of age,25 or an adult, whether she was single or married. And it applies even if the Jew was a minor of nine years old, she is executed.26יאֲבָל יִשְׂרָאֵל שֶׁבָּא עַל הַגּוֹיָה – בֵּין קְטַנָּה בַּת שָׁלוֹשׁ שָׁנִים וְיוֹם אֶחָד בֵּין גְּדוֹלָה, בֵּין פְּנוּיָה בֵּין אֵשֶׁת אִישׁ, וְאַפִלּוּ הָיָה קָטָן בֶּן תֵּשַׁע שָׁנִים וְיוֹם אֶחָד – כֵּיוָן שֶׁבָּא עַל הַגּוֹיָה בְּזָדוֹן, הֲרֵי זוֹ נֶהְרֶגֶת, מִפְּנֵי שֶׁבָּאת לְיִשְׂרָאֵל תַּקָלָה עַל יָדֶיהָ, כַּבְּהֵמָה.

This punishment is explicitly mentioned in the Torah, as Numbers 31:16-17 states: “Behold they were involved with the children of Israel according to the advice of Balaam…27 Execute any woman fit to know a man through lying with a male.”

Source : Issurei Biah – Chapter Twelve