Why does any state allow marriage
 

for those under 16, 17 or 18........take your pick......with a parents consent or the approval of the court?

what age do you think it should be? whatever you pick, there will be some who think it is too young or too old. and then there will be the outliers and anecdotal examples that don't fit (at least according to some). so the states put the parental consent caveat in there.

so a polygamist parent
 

gives consent. Legal?

So what would be your minimum legal age, exUte?

This is a hard question because we attach statutory rape to these ages. Personally, I'm opposed to the archaic non-forced rape statutes and the legal age of consent with a parent's permision. If a parent wants to give permission at 3 for his kid to be married to another kid and then have it consummated at a later date (as is common in many cultures) we shouldn't have statutes forbidding it.

Are they giving consent or are they forcing the child into marriage? There is a big difference.