Friend getting married at 18

Anon because some friends are on here who know my username and I'd rather not cause any conflict/gossip/whatever. A close friend who I've known since we were very young recently got engaged. She turned 18 a few weeks ago, and has been dating her now fiance for about 6 months. They want to get married in the summer, then live together when they are at uni (they're renting a small house). I think they are a good couple... but they've been together for such a short amount of time :S obviously I want her to be happy above all else, but it just seems unnecessary to me. If they break up, like a lot of couples our age do, they'll have a house and a divorce to sort out! I can't see much of a point to them getting married - they're moving in together, surely that's enough of a commitment! I can understand them wanting to celebrate their love for each other, but I can't get over how fast it's all happened... I'm not sure what to say to her, really. I'm trying to be supportive but I can't get over my doubts about it. It just seems strange to me that she's marrying so young in this day and age, and all of our mutual friends are of the same opinion. I don't want to strain our friendship or anything, but I want to make sure she really knows what she's letting herself in for, and that she really wants to do it - I'm worried that she might have felt obliged to accept her boyfriend's proposal because he'd gone to a lot of trouble about it and bought a ring etc. Should I say something to her about it, and how can I do it tactfully? Am I right to have all of these concerns about it or am I over thinking what should just be a happy occasion? I'd be grateful for advice/opinions. Sorry for the rambling post, this is all just very confusing!

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