If the marriage of a child is arranged by his or her parents and the nikah is announced, then when the child comes of age, the child has the right to decline the marriage and have it dissolved as their ‘right of maturity.’ (Fiqh Ahmadiyya, vol, 2 p. 90–93)
This is similar to how we dedicate the lives of our children for the service of Islam through Waqf-e-Nau, but for the Waqf to be finalized they must rededicate themselves of their own choice when they reach maturity.
When we hear the words “underage marriage,” a very different picture may come to our minds than what Islam has actually permitted. Only the nikah of a child can be announced, but the marriage cannot be consummated. Only after the child has reached maturity and decided for him or herself is the marriage finalized (Fiqh Ahmadiyya, vol. 2, p. 90–93).
The nikah of the son of the Promised Messiah as, Hadrat Mirza Mubarak Ahmad, was announced with Hadrat Syeda Maryam ra when they were both still children. One of the reasons for this marriage was:
Perhaps some dreams which, by fulfilling them literally, it was hoped that their messages of warnings could be changed .(Anwarul ‘Ulum, vol. 17, p. 348; Meri Maryam).
In the interpretation of dreams, if it is seen that someone is getting married, one meaning is the nearing of his death (Ibn Seerin’s Dictionary of Dreams According to Islamic Inner Traditions, p. 267).
Such dreams were seen about Mirza Mubarak Ahmad. Thus, along with prayers that he be saved from the metaphorical meaning of the prophetic dreams, his nikah was also announced in hopes of fulfilling those dreams literally. However, it was destined that they ultimately be fulfilled metaphorically with the demise of Mirza Mubarak Ahmad soon after.
The circumstances under which the Promised Messiah as announced the nikah of his son show that it was an exceptional case, but the fact that he did it shows that it is not forbidden in Islam. If a person in the United States wanted the nikah of their child announced as an exception, they would need to request permission from Hudur aba.
The legal age of marriage varies with time and place. Only a hundred years ago in the West, a person could legally marry at 12 years of age or even younger. In some states laws such as this still exist. These days, the minimum legal age is generally 16–18, but it is possible that a hundred years from now it will have changed to 25.
These ages are decided based on the circumstances of each country. If we find the age decided upon by another country in another time to be objectionable based on our circumstances, it would be like if the age we have decided upon now was found objectionable by people in the future based on their own circumstances.
The only minimum age that Islam has set is for the consummation of marriage, not the legal marriage. This age is the one taught to us by nature: sometime after the starting of menses for women and nocturnal emissions for men. After this age, a country or community can set an age that best suits its needs as the minimum age for the consummation of the marriage (Fiqh Ahmadiyya, vol. 2, p. 20).