If they're so in love, they can wait.
People in the South tend to get married at a younger age, and they tend to divorce in a higher rate than elsewhere as well. The link between young marriage and early divorce aren't accidental.
Child marriages were fairly commonplace in the United States up until a century ago. You know, like back in them Little House on the Prairie days, well there was a shortage of women, a severe shortage of women. Men went West. Women, not so much.
So what few females there were, were in high demand, and that very much included the underage. That wasn't like they were all really young, but 10 and 12-year-old brides weren't exactly unheard of back then either.
It was Liberals/Progressives back East in them cities that started pushing to raise the age of consent and marriage to end this practice. 18 as legal is a rather recent phenomenon, historically speaking.
So when we say that Muslims are behind us with this, they are. By an entire gigantic whopping whole huge century. A century. And if it wasn't for Progressives, it would still be common. Right now, today, there are more child marriages in the South than there is up North. Today. Conservative values, you see, are a little bit broader than we typically are led to believe.