Young Marriage in the South?

I've always wondered why it's such a huge tradition in the south to get married young, in particular to men entering the armed services. Case in point, a distant cousin of mine was telling me how her granddaughter got married right out of high school to her fiancee who's in the army and is traveling to Germany. My distant cousin got married when she was 18, her daughter at 18, and now granddaughter at 18. I'm 21 and everyone I know around me is getting married and it makes me sensitive about being single because I want to find someone to be with for a long time whether I get married at my age or not (although I'd like to be married around 25-27ish). I've had young married couples who have very good marriages tell me it's rude to criticize them because they married so young (family members that is) yet these people turn right around and ask me in a very condescending manner when I'm getting married? Talk about being rude! Do I look like I know when I'm getting married? No, maybe when Christian Bale's available I will. But anyways, why is it such a huge deal to marry young in the south?