Getting married to my best friend at 21?

my fiance and i have been together for 4 months living together for only 2 months. I moved accross the country to be with him and we are very happy. we talk about everything and have the fundamentals to have an amazing long lasting relationship.Weve been close friends since we were 10 and its really easy for us to be with one another. He is in the marines and we have decided to get married but my parents strongly disagree. my brother who is 10 years older than me aproves and thinks that given all the facts its a wise decition. My parents like my fiance but think we need more tome to make a decition like this. we are both wiser than our years and can see ourselves together forever. we want to have a small courthouse marriage with just the two of us and when we return home have a second ceremony for our friend and family. i love my family but I want to make my own decitions without hurting anyone..... should I marry him without my parents consent?