Christianity and its morals.
Isaac’s wife was Rebecca, mother of Jacob and Esua. According the calculations made by Rabbi Solomon Itzhaki (A.K.A. Rashi a well-known respected Jewish Scholar), Rebecca was three years old when she married Isaac.
1. Rashi’s commentary on Genesis 25:20 says:
forty years old: For when Abraham came from Mount Moriah, he was informed that Rebecca had been born. Isaac was then thirty-seven years old, for at that time Sarah died, and from the time that Isaac was born until the “Binding” [of Isaac], when Sarah died, were thirty-seven years, for she was ninety years old when Isaac was born, and one hundred and twenty-seven when she died, as it is stated (above 23:1): “The life of Sarah was [a hundred and twenty-seven years.”] This makes Isaac thirty-seven years old, and at that time, Rebecca was born. He waited for her until she would be fit for marital relations-three years-and then married her.— [From Gen. Rabbah 57:1
[Retrieved it from this website: http://www.chabad.org/libra…/bible_cdo/…/8220/showrashi/true]
2. Also Johann Buxtorf cites Rashi that Rebecca was three years old when she married Isaac. Do focus carefully on the words:
“Rabbi Solomon in his comment on Genesis, says that Rebecca, when she was married to Isaac, was but three Years of Age. His words run thus, ‘When Abraham was come from Mount Moria, he received the joyful News of Rebecca. Isaac was at that Time Thirty seven years old; and then did Sarah die. The time, from birth of Isaac to the death of Sarah, was Thirty seven Years, And Sarah was Ninety Years old when Isaac was born; and One Hundred and Twenty Seven Years old when she died: As it is said in Gen 23:1 . Sarah was one hundred and twenty-seven years old. Behold, the Age of Isaac was Thirty Seven Years, at the Time of the Birth of Rebecca. And when he had waited for her three Years, till she was fit for marriage, he took her to wife.”
According to this Account, Rebecca was a very notable Girl at three years of age. But that a girl of three Years old is fit for marriage, is maintained very plainly in the Jewish writings; particularly, in Emek Hamelech, in the following passage, ‘our blessed sags, of blessed memory, say, that a female is not fit for marriage, ‘till she is arrived at the Age of three years and one day.’ The Talmud supports these Sages here, in the part entitled Avoda Sara. And the Sanhedrin says, A daughter, who is of the age of three years and one day, is, by being bedded with a Man, lawfully married.” 
Before going any further, one of the objections raised by some Jewish and most Christian Apologist is that they say: “how can a three year old fetch water out of a well?” They further say: – “a girl of that age could not do that she must be a lot older than three.” These statements do not disapprove anything. The way they make it seem, as if it is impossible for a girl to pull 1, 2 letters of water. Any three old girl could pull 1, 2 letters of water out of a well, is not rocket science.
I have a challenge for you people, if it is impossible for a three-year old to pull out 1, 2 litters of water – bring me some solid proof (evidence) that a 3-year-old girl could not do that.
3. In addition to what we have already brought forth on Isaac’s marriage to Rebecca, The Zohar 1:136b Pritzker Edition. Volume two which is Translated/Commentary by Daniel Chanan Matt also makes mention that Isaac married Rebecca when she was three years old:
51. “She was three years old when he embraced her the youngest legal age a female can be-married. See M Niddah 5:4; Seder Olam Rabbah 1; Soferim, add. 1:4 Rashi on Genesis 25:20 Tosafot, Yevamot 61b, s.v. ve-khen; sekhe; Tov, Genesis 24:14.
Rebekah’s three years correspond to the three colors of the rainbow.
52. He engendered at sixty, generating fittingly… see Genesis 25:26.
When Isaac fathered Jacob he was sixty years old, symbolizing the full sextet of sefirot from hesed through Yesod, thereby ensuring that Jacob would be complete. 
As you have read it is quite clear/fact that Rebecca married Isaac when she was three years old. Furthermore we have more evidence from Judaic Holy Book ‘Mishnah’, it gives more weight to the above references that girls as young as three years old were allowed to be betrothed by intercourse at the age of three. Although in Ancient Hebrew marriages girls were recommend to be married at the age of 12, there are laws in the Mishnah that give approval that once betrothed you can have sexual intercourse anytime after the age of three years old.
4. Jacob Neusner is an American academic scholar of Judaism. In the Book: ‘The Comparative Hermeneutics of Rabbinic Judaism: Seder Tohorot. Tohorot through Uqsin.’ The Jewish oral Torah i.e. Mishnah says:
M. 5:4 A girl three years and one day old is betrothed by intercourse. And if a Levir has had intercourse with her, he has acquired her. And they are laible on her account because of the law [Prohibiting intercourse with] a married woman. And she imparts uncleanness to him who has intercourse with her [when she is menstruating] to convey uncleanness to the lower as to the upper layer. [If] she was married to a priest, she eats heave offering. [If] one of those who are unfit [for marriage] has intercourse with her, he has rendered her unfit to marry into priesthood. [If] one of all those who are forbidden in the Torah to have intercourse with her, he is put to death on her account, but she is free of responsibility. 
 Johann Buxtorf, Johann Andreas Eisenmenger, John Peter Stehelin
Rabinical literature: or, The traditions of the Jews, contained in their Talmud and other mystical writings. Likewise the opinions of that people concerning Messiah, and the time and manner of his appearing; with an appendix comprizing Buxtorf’s account of the religious customs and ceremonies of that nation; also, A preliminary enquiry into the origin, progress, authority, and usefulness of these traditions; wherein the sense of the strange allegories in the Talmud and Jewish authors is explained. [ Publisher: London J. Robinson, 1748] Volume 1 page 33 – 34
 The Zohar: Pritzker Edition. Volume two, (2003) page 264 [The Zohar 1:136b] Translation and Commentary by Daniel Chanan Matt
 The Comparative Hermeneutics of Rabbinic Judaism: Seder Tohorot. Tohorot through Uqsin By Jacob Neusner Volume 6 [Copyright 2000] page 152
(Please Visit for more details on the subject)