Marriage was a good idea for me when I was 24 - 25 and that is why I got married when I was 25 (on my 25th birthday). But it would have been a very bad idea for me to get married at the age of 17 - 18 (I was unstable at that age and immature).

So in summary, it doesn't matter if God created the concept of marriage or if man did. Sometimes it's a good idea to get married and sometimes it's not.