Too many people rush into marriage. It takes time to get to know someone, like really get to know them. Everyone is on their best behavior when they begin dating. And since it takes time to know someone's lifestyle, meet their friends, earn their trust and fall in love, there is no benefit of rushing into marriage.
I would never even consider marrying anyone after knowing and dating them for less than five years. In five year's time, you get to learn a person's habits, if there is mutual respect and trust, how they handle their money, their ethics and morals, how they handle stress, distress and how they treat their family and even how they treat waitresses.
If people are IN love, then hopefully they will be in love for a good long time. So, there is no point in rushing into anything if you intend to plan your whole lives together, because you ARE together.
While I have your attention, I seriously do not think anyone should marry under the age of 25, maybe 30. Yeah, you may think I am nuts, but young adults need some life experience after college before making a lifelong commitment.