It may be possible that in some cases by the age of 14...
It may be possible that in some cases by the age of 14, a girl may be mature enough to shoulder the responsibility of family-life and motherhood, but a woman of 30 may not yet be mature enough to do so! Therefore, what is important in determining the ripe age for marriage is one's own level of maturity and readiness, whether one has reached the legal age for marriage or not!
It would be very naive to ignore geographical and regional conditions and norms, as well as the needs of the youth of the day, and such negligence could lead to many problems.
In the present world, with the greater intermingling between sexes, better nutrition, educational facilities and more awareness due to advanced mass media, children are reaching "maturity" much earlier than ever before; and considering these factors, raising the legal age for marriage for boys and girls is quite unjustifiable.
It is interesting to note that at one point of time, the British Parliament had passed a law that had set the minimum legal age for marriage of boys at 21 years, whereas the minimum permissible age for being candidate for the post of Prime Minister was 18 years! When the people raised an objection to this absurd law, the Parliament responded by declaring that it was often more difficult to manage a wife than to manage a country.
Raising the legal age of marriage and not permitting young boys and girls who are dealing with strong sexual urges, to have a healthy and safe outlet for their natural, youth-related tendencies, only leads to the spread of promiscuity and moral corruption in the society.
If boys aren't allowed to form a family before the age of 18 or 20 years; or if girls are forced to face emotional and psychological pressures due to the same reasons, then they become very prone to social and psychological problems. Thus, we conclude that a suitable age for marriage would be the time of physical and mental maturity in a person. Islam has specified the age of physical maturity but it has not specified the age of mental maturity.
Rather, it has left it open to the discretion of the parents and children themselves. Those who are in favor of raising the legal age for marriage argue that: Boys, before the age of 18 and girls, before the age of 15 aren't equipped to form a family and aren't in a position to bear the heavy responsibilities and difficulties of family life. Early marriages are a contributing factor to criminality.