what does a 20 year know about marriage?
Nothing...marriage hasn't changed, but the people have.
What Gen X and Millenials know of marriage is limited to divorce, TV/Entertainment/Pop culture.
It's funny hearing people describe their signif others as "my fiancé", and they have only been dating 6-7 months. Marriage has been so downgraded, that a fiancé tends to have a looser meaning (sometimes it goes as far as "we talked about it").
And let's not forget, the dude this young lady married is 27...