I believe that it's best for people to wait until around age 25 before thinking about marriage. It seems to me that a lot of people go through a "shift" around that age. That's been the case with myself and the people I come into contact with, anyway. Keep in mind that the population I'm talking about has at least a Bachelor's degree; so you're talking about people who live as students until around 22, then struggle with trying to figure out what to do/be for a few years after that, which puts you at about 25 when you start to feel like you know who you are, and what you want out of life. People who hit the ground running at age 18 may experience that "shift" earlier; I don't know.
My point is that, if you lock yourself in before you hit that shift, when you come out on the other side of it, you could discover that who you are now just does not mesh with the person sleeping next to you! <img src="/images/graemlins/shocked.gif" alt="" />
But I think that whether a marriage lasts or not has less to do with age than with things like how you see your life, why you think you're here on this planet, and what your concept of marriage is.
For example, I was engaged at 19, married at 21, and divorced at 25. The reason I married so young was that I was going to school across the country from my family and friends, and felt too alone for my own comfort. I didn't realize it at the time, but in looking back, I can see that I latched onto my ex-husband as a way of creating a family and home base for myself where I had none. (I also thought the whole point of going to college was to find a husband, but that's another issue entirely! <img src="/images/graemlins/rolleyes.gif" alt="" />)
I knew almost instantly that I wasn't completely happy in the marriage, but I dismissed those feelings. Over the next few years, the feelings grew, and I continued to dismiss them, because my belief system was such that I accepted the unhappiness a natural part of marriage.
In my opinion, if you hold this belief -- and I think a lot of people do -- you can stay married for 60 years to the same person, but that doesn't mean you should have, or that you really spent your life with your ideal partner! It's an "I made my bed, now I have to lie in it" mentality. And I wouldn't want anyone to stay with me forever if that's how they viewed their life with me! <img src="/images/graemlins/queen.gif" alt="" />
I'm now 39, and have been with the love of my life for 13 years. We have our ups and downs, but we always work them out. Is it working because I met him when I was 26? Is it because I got the "need to get married/gotta plan a wedding" garbage out of my system before I met him? Is it that I met him after my shift? Or is it just that he is "the one," and no matter when I would have met him, we would have clicked, and it would have lasted?
As they used to say in the Tootsie Pop commercials, "The world may never know. . . ." <img src="/images/graemlins/lovers.gif" alt="" />