I'm 22 and married. We chose to get married because we love each other and know that this is what we want. We didn't do it just to say oh hey I'm married. We knew what we were getting into and actually know that we're in this forever. Wasn't in a rush, or running from anything and we were fully supported by our families. Yeah, we're on the younger but we went into this fully aware of what it means.
I got married at 19. I'm Muslim and my religion encourages us to marry young so we avoid falling into the trap of fornication which is a sin in Islam. Also my family wanted me to go to college and I had no desire to go to college. My family also hates Muslims and as I'm the only Muslim in my family I faced and still/will always face difficulties for my faith so partly why I got married is because I knew it would be easier for me as a new Muslim to practice my religion if I got married. Plus I was ready to settle down and start a family.
Canada is part of North America. Do you mean a U.S. thing?
To answer your question, I think there are a lot of reasons. For some, it's related to religious upbringing, for others it's a way to escape an unpleasant home life, for others it's just because they met the right person at a young age. For some it's because they got knocked up and decided to get married. Just like there are all kinds of reasons for waiting until a later age. Personally, I was 25 when I got married--my husband and I had been together for three years, we knew we wanted to build a life together, and we were ready. I wasn't in a rush to get married, that was just when it happened.
I do think it's important to recognize, however, that by the standards of a lot of other cultures, particularly non-Western ones, the North American average age at first marriage is actually quite late. I suppose it would seem early if you're looking at things through a very narrow, Western lens, but if you widen your view to be more global, the average here doesn't seem that early anymore.
I meant only in North America.
It's not an "American thing". People marry young all over the world.