The Laws of that land do. If you do not like them, do not travel there or if you live there, work to get them changed. But every country has the right to make what ever laws they want. In some countries girls are permitted to be married as young as 11. 12 being fairly common. But keep in mind..to stay on topic, it is mostly "men" who are making those stupid young age laws. In the US I am thinking the youngest age anyone can get married is 16 of any state. But I may be wrong.