The Bible gives no age of consent for sex. It simply teaches that sex must be a loving, lifelong one-flesh union between a man and a woman who are not otherwise related (see Leviticus 18 for who is ruled out by that requirement). If these conditions are met, maturity and age disparity become less of a moral issue than an issue of whether the relationship is wise based on other factors.
While there are no authoritative moral prescriptions on an age of consent, it is worth investigating to see how the Bible’s ethic was put into practice, and how age factored into marriage in the Biblical world. While we often hear claims that Joseph and Mary were fifteen years old or even younger, we have no compelling evidence as to how old either of them were. In the same list of landmark ages that gives us thirteen as the “Bar-Mitzvah” age for fulfillment of the commandments, the Mishnah declares eighteen as the age when a man is ready for the bride-chamber (Aboth 5:21).
But prepare for a shock. The rabbis in the Mishnah also declare that a girl may be legally betrothed by intercourse as early as age three (Niddah 5:4). The age that a boy can contract a valid marriage appears to be age nine (Niddah 5:5 and other passages). But such ages in the Mishnah are usually given as hypothetical cases. We must also understand that “betrothal” means a legally binding virtual marriage that can only be broken off by divorce. Furthermore, betrothal was almost always done in writing rather than by intercourse, after which the couple continued to live apart for normally a year before they moved in together, accompanied by a public celebration and feast. So it is highly unlikely that three-year-old girls were actually taken as brides.
A more significant age benchmark, from our modern point of view, would have been age twelve and a half, the age at which a girl is no longer a minor and can refuse her father’s choice of a mate for her. (See the Talmud, b. Kiddushin 2b, 79a.) We might call this a reverse age of consent (!). Still, in Biblical times, the father’s authority continues over a girl on all other legal matters (he can cancel her vows and keep what she earns) until she moves in with her husband. And the girl cannot legally betroth herself until age twelve.
Age three was the age at which some Jews calculated that Rebecca married 40-year-old Isaac. This claim is based on baseless assumptions about timing. The details are left unspecified in the Biblical text, but Isaac’s age (Genesis 25:20) permits time for Laban to grow up and have a teenage daughter after Genesis 22::20-22.
One more curious detail about the ancient Jewish approach to “under-age” sex and the age of consent: before age three, any girl who had had sexual contact was still regarded as a virgin. Virginity was considered “recoverable” at this point (Niddah 5:4). This belief did not necessarily deny the hideous trauma of such a violation, but simply declared that such a victim should be considered a virgin with all the rights that go with that status.
The Talmud indicates that young men were expected to marry any time from sixteen to 24 years of age, depending on which rabbi is cited. Age 20 was the most common opinion. One rabbi stated, “He who is 20 years old and is not married, spends all his days in sin.” In other words, for a man to remain unmarried past this age was considered an open door to temptation.

The legal age of marriage in Roman law was twelve (Codex Iustinianus 5.4.24), with engagement permitted at ten by Augustus, later to be moved to as young as age seven. (See references in Balsdon, Life and Leisure in Ancient Rome, 380, footnote 117.) Balsdon (121) cites a study of 145 inscriptions which shows that eight per cent of middle-class Roman women married before age twelve, ten percent at twelve, and eleven percent at thirteen, leaving the remaining 71% to have married at ages fourteen or older.
Age of consent and cross-generational marriage are issues we need to address from a standpoint of prudence rather than morality. The Bible’s teaching that reserves sex for a lifelong loving one-flesh union of a man and a woman is our moral bedrock. For a 40-year-old man to marry a fourteen-year-old girl may be acceptable from a purely moral standpoint, but may be questionable from a wisdom standpoint: will it work out? And the question of whether a teenage boy or girl is emotionally mature enough for a sexual relationship of any kind cannot be answered with a one-size-fits-all answer; it will vary by cultural situation and by personal factors.
I believe the ideal application of the Biblical sexual ethic would be to prepare young people for marriage as early as possible within the realities of our cultural context. We are told that it is unrealistic to teach young people to save sex for marriage, because we assume that will mean they must wait until they are past college and are established in their careers. I would argue it is unrealistic to pressure them to wait that long until marriage. I believe we should make it easier for our young people to enjoy marriage, by preparing young people for full adult responsibilities by the time they begin college, like numerous other cultures do. Better to make it more practical for them to marry younger, than to set aside God’s sexual ethic.