But should you assume that marriage is still out of the question when you're 25? Twenty-seven? I'm not suggesting that you decide ahead of time that you will get married in your 20s. You've got to wait until the right person comes along. I'm just pointing out that you shouldn't exclude the possibility. If you wait until your 30s, your marriage is likely to be a merger. If you get married in your 20s, it is likely to be a startup.
Merger marriages are what you tend to see on the weddings pages of the Sunday New York Times: highly educated couples in their 30s, both people well on their way to success. Lots of things can be said in favor of merger marriages. The bride and groom may be more mature, less likely to outgrow each other or to feel impelled, 10 years into the marriage, to make up for their lost youth.
But let me put in a word for startup marriages, in which the success of the partners isn't yet assured. The groom with his new architecture degree is still designing stairwells, and the bride is starting her third year of medical school. Their income doesn't leave them impoverished, but they have to watch every penny.
What are the advantages of a startup marriage? For one thing, you will both have memories of your life together when it was all still up in the air. You'll have fun remembering the years when you went from being scared newcomers to the point at which you realized you were going to make it.
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Marry someone with similar tastes and preferences. Which tastes and preferences? The ones that will affect life almost every day.
It is OK if you like the ballet and your spouse doesn't. Reasonable people can accommodate each other on such differences. But if you dislike each other's friends, or don't get each other's senses of humor or—especially—if you have different ethical impulses, break it off and find someone else.
Personal habits that you find objectionable are probably deal-breakers. Jacques Barzun identified the top three as punctuality, orderliness and thriftiness. It doesn't make any difference which point of the spectrum you're on, he observed: "Some couples are very happy living always in debt, always being late, and finding leftover pizza under a sofa cushion." You just have to be at the same point on the spectrum. Intractable differences will become, over time, a fingernail dragged across the blackboard of a marriage.

And last, but not least, watch Groundhog Day a lot.

Without the slightest bit of preaching, the movie shows the bumpy, unplanned evolution of his protagonist from a jerk to a fully realized human being—a person who has learned to experience deep, lasting and justified satisfaction with life even though he has only one day to work with.
You could learn the same truths by studying Aristotle's "Ethics" carefully, but watching "Groundhog Day" repeatedly is a lot more fun.