Joseph,
That was not my question. My question was ” Why is an 18 year old girl who is too immature to know what kind of man she wants to marry looking to get married? ” If the girl was mature, then fine. That is the reason why you cannot be a posek. You cannot apply a principle like a blanket to all people. This girl, and others like her who have no clue about the responsibilities and stresses that married life brings, is not ready for marriage at that young of an age.