A Saudi cleric who is ostensibly an expert on marriage has offered several fascinating opinions on the subject, and in his bizarro world, girls as young as one year old can be married "provided sexual relations" are delayed: http://www.memritv.org/clip/en/1798.htm. The transcript of the interview follows, but if this isn't an incredibly good example of just how backward thinking the Saudis are, then I don't know what is:
Dr. Ahmad Al-Mu'bi: Marriage is actually two things: First we are talking about the marriage contract itself. This is one thing, while consummating the marriage – having sex with the wife for the first time – is another thing. There is no minimal age for entering marriage. You can have a marriage contract even with a one-year-old girl, not to mention a girl of nine, seven, or eight. This is merely a contract [indicating] consent. The guardian in such a case must be the father, because the father's opinion is obligatory. Thus, the girl becomes a wife... But is the girl ready for sex or not? What is the appropriate age for having sex for the first time? This varies according to environment and traditions. In Yemen, girls are married off at nine, ten, eleven, eight, or thirteen, while in other countries, they are married off at 16. Some countries have legislated laws forbidding having sex before the girl is eighteen.
The Prophet Muhammad is the model we follow. He took 'Aisha to be his wife when she was six, but he had sex with her only when she was nine.
Interviewer: When she was six...
Dr. Ahmad Al-Mu'bi: He married her at the age of six, and he consummated the marriage, by having sex with her for the first time, when she was nine. We consider the Prophet Muhammad to be our model.
Interviewer: My question to you is whether the marriage of a 12-year-old boy with an 11-year-old girl is a logical marriage, which is permitted by Islamic law.
Dr. Ahmad Al-Mu'bi: If the guardian is the father... There are two different types of guardianship. If the guardian is the father, and he marries his daughter off to a man of appropriate standing, the marriage is obviously valid.
People find themselves in all kinds of circumstances. Take, for example, a man who has two, three, or four daughters. He does not have any wives, but he needs to go on a trip. Isn't it better to marry his daughter to a man, who will protect and sustain her, and when she reaches the proper age, he will have sex with her? Who says all men are ferocious wolves?