From the Ask the Imam website:
Question: i am 45 and married to already 15 years now after the sexual desire of my woman has nearly gone i am looking to marry again. And i would like to marry a woman who is 12 years old, her father and she has also agreed, my first wife told me that it could make problems if it will be a big different in age, and also some of my children are older than my second wife. What is your advise ? And is it allowed for me to have already sexual intercourse with these woman after we are married or to i have to wait till she reach at special age ?
Answer: According to the Shari’ah, if a girl is a minor (did not attain puberty), she may be given in marriage by her father. When she attains puberty, she has the right to maintain the marriage or discontinue the marriage. There is no age limit to be intimate with one’s wife even if she is a minor.
It is important for you, in your situation, to consider the age difference reservation expressed by your wife.
and Allah Ta'ala Knows Best
Mufti Ebrahim Desai
Source:
http://islam.tc/ask-imam/view.php?q=6737