Just comfort yourself knowing that the reasons they are marrying and have chosen the person they have are not ones that usually make a solid foundation for a marriage.
When I look back at myself upon finishing college, I know that I was sooo far from ready to get married, and your priorities and standards for a mate change a LOT between 18 and 25 or so. I look around at my church now & see people my age mostly married with children, and the single guys my age dating 20 yr olds. It makes me feel like a spinster sometimes (and I'm not even 30
), but I wouldn't trade the refinement I've gone through the past couple years alone to be stuck in a marriage with someone who I liked at 21, but who is terribly wrong for me as a lifelong partner. And I see that in some of those people's faces too....