The Torah does not specify an age at which a girl or boy can become married. Betrothals can happen even at infancy; but the age of consumation is not specified.
Fear not though! The principles in the Torah can enlighten any topic.
In Islam, a girls first menstruation is considered to mark her sexual availability. The prophet Mohammed himself consummated his marriage with Aisha when she was nine years old. This does not seem right. The incidence of infant and mother mortality among young mothers (those under the age of 18) is so much higher than that of mature, adult women, that it seems any humane person would outlaw marriages of underage girls.
But what does the Torah say?
Isaiah 65:22 They shall not build, and another inhabit; they shall not plant, and another eat: for as the days of a tree are the days of my people, and mine elect shall long enjoy the work of their hands.
I ask you this, which is more precious, the fruit of a tree, or the fruit of the womb? Throughout the Word, children are spoken of the fruit of the womb. A good wife is spoken of as a fruitful tree, a fertile vine (Ezekiel 19:10, Psalm 128:3). God's people are told their days will be like those of trees.
Since we are compared to trees, perhaps God's laws about trees will apply. When is a tree considered ready for harvest?
Leviticus 19:23-25 And when ye shall come into the land, and shall have planted all manner of trees for food, then ye shall count the fruit thereof as uncircumcised: three years shall it be as uncircumcised unto you: it shall not be eaten of. But in the fourth year all the fruit thereof shall be holy to praise the LORD withal. And in the fifth year shall ye eat of the fruit thereof, that it may yield unto you the increase thereof: I am the LORD your God.
You can see here, the tree was not to be harvested until the fifth year after it started producing fruit. A tree that is not pruned with an eye to immediate harvest during its first three years becomes immensely stronger and healthier. At the end of that time period, it produces such a bounty of fruit as to shame its sibling who was put to work from the very beginning. If a tree, which produces delicious and excellent fruit, merits so much forbearance and care, how much more our sisters and daughters, who will produce the next generation of our race, and keep our ancestors names from dying out?
For a human female, five years after the start of menstruation is universally agreed by developmental physiologists to be sufficient time to physically mature and safely bear children. Science tells us that most women are not able to get pregnant until as much as a year after the start of menstruation. Science also tells us that women's bodies do not finish developing for at least five years after the start of menstruation.
Let any woman reading this reflect; did you feel fully developed the day your menstruation started, as the Muslims insist you were? Or was it five years later, as Moses said?
Not so long ago, the average age of menstruation was 11. Should it seem strange that at that period of time people often spoke of a girl who was "sweet sixteen"? Sweet sixteen was considered to be a "ripe" and marriageable girl. In other times, menstruation started in a womans late teens. In those times and places, the average age of marriage was in a woman's early twenties, five years after the start of menstruation. It seems that Western human beings have instinctively felt for many centuries that which the Torah proclaims in symbols.
When a man goes in unto a virgin, he "pops her cherry". Who likes to eat green cherries? Such a man will break his teeth, and the seed inside the fruit will not sprout and multiply. What should Western countries do about Muslims who prefer such unripe fruit? Are they any different from those who lust after the golden apples of Eris and Iduna?
The God of the Torah is the ultimate fertility God. He doesn't just care about the quantity of life a woman can produce through childbirth; he cares how much of that life will survive into adulthood, to breed more life in its turn. He sees the big picture. Healthy babies that survive their childhood are important to him. Healthy mothers who live long lives and help their children succeed are even more important to him.