Sounds like we are in similar spots. I first want to say that it is good to know that I am not alone in this!
There are multiple reasons that we are wanting to get married sooner. We have been together since high school, 5 1/2 years now. And for at least 2 of them, we have discussed marriage as a possibility. I'd be lying if I said it wasn't just to start living married life. That is definitely a part of it.
For one, we are both extremely religious, so of course the sexual side of things is a factor for us. But also, financially we believe that we would be better off if we are able to have a year to stabilize ourselves. That way we can become comfortable with each other and the roles that we will each play in the marriage (i.e. who handles finances, etc, etc).
I suppose you could say that it runs in my family to be married young. My grandmothers were 16, and my mother was 17 when they were married. My mom's biggest concern is that I won't graduate college, and I'll miss out on the opportunities that she missed out on. She chose my dad over school (I didn't come along for 3 years) and he was in the Air Force, so there wasn't any real "home" for them for quite some time. I suppose that is something that you may have to consider, as well, seeing as Ben is a military man himself.
I would have to say that, for me, the main reason that I want to get married is because I think it is important to have to struggle a little bit as a couple, because that will make us depend on each other for more things, and will allow us to grow much closer. I believe that is what will make our marriage a firm foundation. As I said, we are both very religious, so we don't believe in divorce, we'll marry for life, so I want to have every chance in the world to make it a happy union.
I hope that answers your question. I'd be interested to find out what the two of you decide. Also a question, why would you want to keep it quiet if you do go ahead with it?