Second marriage possible under these conditions. i would like to marry a woman who is 12 years old, her father and she has also agreed. What is your advise?

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 ?