Marriage is a very cultural institution. The acceptable age depends a lot on the culture you have grown up in and the social norms around marriage. Personally, as an American, I think waiting until 22 or later is a good idea because our culture, in general, places a high value on individualization and less so on commitment. Individualization taken to extremes is not as good for marriage as commitment is! So in the case of marriage in the USA, I think it better to wait until the person as matured enough to recognize the need for commitment in marriage.