Getting married at 18?

Hi :) do I was wondering what your guys opinion was on getting married at 18? My fiancé and I have been together for 3 years in June, it would be 4 years when we get married, we have a 2 year old son, and have been living together for over a year now. We live at my parents, but we pay rent, but our own groceries, do everything you would living in your own place, and we are getting our own place next month. He has a full time job, and I’m starting a photography business. We make $2,613/month, and my parents aren’t supporting us financially at all, if anything we are supporting them. But we have been talking about getting married for just over a year now, and obviously we wouldn’t be having a crazy expensive wedding, but to me it’s not about how expensive it is, it’s about sharing that experience and memory in your life with family and friends, but I’ve heard a lot of things about getting married really young, and how people say it won’t last, but we are already acting as if we were married, just don’t have the papers. We share bills, make decisions together, I deal with the money, we don’t argue about “well that’s my pay check, my money”. I know a lot of people say once you get married everything changes, but I don’t see how getting a piece of paper will change anything? We already live together. But anyway, I guess I’m asking if any of you think it’s a bad idea? My family don’t know that we are thinking about it yet, but all of our friends know, I’m kind of worried about how my mom and step dad will react, especially how my grandparents will react, and I want them to be supportive. But now I’m kind of nervous about the whole thing because of the stories people have.