How old Was Rivka on her wedding day?

The idea that Rivkah was a mere three years of age when she married 40-year old Yitzchak is old and often repeated. Rashi cites it, and so do many others Great Names. (Their reasoning is in the footnote)

But every year I have the same complaint: Why is the fantastic tale of a toddler marrying a patriarch taught as fact, when the matter is far from clear?

Start with the Ibn Ezra. In his comment to Genesis 22:4, he argues, rather convincingly that Yitzchak was not 37 years old at the Akeida. This matters, because the math Rashi uses to prove that Rivka was three, depends on Yitzhak being 37 at the Akeida. If Yitzchak wasn't 37 at the Akaida, Rivka was not three when she got married. If this doesn't convince you there's more: Read about it: here and here and here If you're feeling especially ambitious visit the Tosfot on Yevamot 61b (“v’chen”)

FOOTNOTE
This is the math that Rashi uses to support his claim that Rivka was three when she married Yitzchak. As you'll see from the other materials I posted, Rashi's math is based on some assumptions that other challenge.

1. Per the posuk, Sarah was 90 when Yitzchok was born.
2.Per the posuk, Sarah died at 127. Rashi speculates (though others argue) that her death occurred immediately after the Akeidah; therefore Yitzchok was 37 at the Akeidah.
3. Immediately after the Akeida, Avrohom hears the news of the birth of Rivkah, so she was born when Yitzchok was 37. This is suggested by the text, but it isn't a slam dunk.
4. Per the posuk, Yitzchok was 40 when he married Rivkah, so if all the other speculations are accurate, she was 3 when they married.