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"Shatha Ali Nasser confirmed that item number 15 in Yemeni civil law reads that "no girl or boy can get married before the age of 15." However, this item was amended in 1998 so parents could make a contract of marriage between their children even if they are under the age of 15. But the husband cannot be intimate with her until she is ready or mature," said Nasser.""

As you note correctly, the Quran doesn't give a lower age limit for the marriageable age of girls. However, it does not directly give an age limit such as 9 years of age for (sexually) "consummating" the marriage. As you probably know, the age of 9 is inferred from the Hadith, as a general guideline, because of Muhammad's consummation of his marriage to Aisha. The guideline is reinforced indirectly due to Quran 33:21 and other verses that state or imply that Muhammad's conduct is exemplary, to be followed by believers. Yet even 9 years of age is not a hard lower limit, because neither Muhammad nor the Quran forbids sex with younger girls. Indeed, either Umar or Uthman--I can't recall which of those "rightly-guided" caliphs--married a four-year-old girl. Moreover, the Hadith state that "enjoyment" of the "private parts" is part of the marriage contract. (Note the 8-year-old girl's statement in the article that she did not know what marriage entailed). The only restrictions from the primary texts, as you note, are vague statements about whether or not the girl is "ready" or, as a hadith puts it, can "take it." Regarding "thighing" and sexual acts with underage girls, some Islamic opinions on this are quoted in Sam Shamoun's article
http://www.answering-islam.org/Shamoun/prepubescent.htm