see
http//misconceptions-about-islam.com/muhammad-married-young-girl.htm
I've looked at the link, this is the test for mental maturity
"And test the orphans until they reach marriageable age. Then if you perceive in them sound judgement, release their property to them. And do not consume it excessively and quickly, that they will grow up. And whoever, , is self-sufficient should refrain ; and whoever is poor - let him take according to what is acceptable. Then when you release their property to them, bring witnesses upon them. And sufficient is Allah." - But how do we know this verse doesn't just apply to orphans?
The verses provided for physical maturity
"And tell the believing women to reduce of their vision and guard their private parts and not expose their adornment except that which appears thereof and to wrap their headcovers over their chests and not expose their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allah in repentance, all of you, O believers, that you might succeed."
"O you who have believed, let those whom your right hands possess and those who have not reached puberty among you ask permission of you at three times before the dawn prayer and when you put aside your clothing at noon and after the night prayer. three times of privacy for you. There is no blame upon you nor upon them beyond these , for they continually circulate among you - some of you, among others. Thus does Allah make clear to you the verses; and Allah is Knowing and Wise. And when the children among you reach puberty, let them ask permission as those before them have done. Thus does Allah make clear to you His verses; and Allah is Knowing and Wise."
Where does it say there that one must reach puberty before marrying?