Child Marriage Was Appropriate Then but Not Now
Why was there child marriage in the old Testament? Isn't that inappropriate?
In some cultures, as soon as puberty is reached, the person is regarded as of an appropriate age for marriage. This is the more ancient and natural practice. In our culture, which seems to require a greater degree of education and autonomy, this would hardly be appropriate. So, for example, Our Lady was between fourteen and sixteen when she bore Our Lord, and the Eternal Father did not regard this as too soon.
The age for legitimate marriage depends on the culture. Nowadays it is eighteen at the earliest, but there are still states where it is possible to marry younger. Current Church law is more strict than civil or common law, although until recently it was not. The key here is prudence and concern for the success of the union in the maturity of the couple. Even today there are some cultures in which early marriage is possible because of the relative maturity and expectations of the parties, but surely in ours that is not the case.