The age of 18 is indeed an arbitrary line. Since there is no way to determine with 100% certainty of mental and emotional maturity, the figure of 18 serves as the best (not ultimate) indicator for legal purposes.
So if you would send your 9yr old daughter to marriage, would you send your 9yr old son to war? Against me when I look like this...
...While your son look like this...
Yes, we can see there is a current exodus of women moving to muslim countries.
---------- Post added at 08:11 PM ---------- Previous post was at 08:09 PM ----------
By my logic? You have a funny way of interpreting people's argument. I think this is because you consistently failed to distinguish the difference between what is 'moral' and 'legal', between what is 'persuasion' and 'coercion'.