I'm in exactly the same boat that you describe, 31 and just about to submit, but i think you're being pretty negative about the situation. When you finish you'll still be (relatively) young and hopefully the economy will have improved, so it should be easier to get a house etc. I have friends/family who are in the position of having to work a job that they hate, just to pay off their mortgage and/or support their kids and believe me it's no fun. It's a kind of 'grass is always greener' situation; I envy their settled lifestyle, whereas they envy my freedom. Most of the people that I know who have done a PhD in the sciences tend to settle down and have families later in life anyway though, so I wouldn't worry about getting stuck behind. You also don't have to do a postdoc. You could use the PhD to go into a much more stable career, if academia and short-term contracts is not your thing.

As far as the social thing goes, I completely understand where you're coming from. When I first started the PhD I left behind my previous job in a really sociable environment. My new lab was friendly enough, but no-one ever socialised after work and outside of the PhD I became pretty bored and fed up. Some new students started soon afterwards though and things changed for the better. That's one of the best things about being in an academic environment, there's always people coming and going so hopefully you'll end up meeting some decent people soon.

Basically what I'm trying to say is try not to get too down-hearted. Like others have said, try joining clubs or try and get other members of the department to go for coffee breaks or to the pub. Also, don't worry too much that you're not as settled as some of your peers. Not everyone wants to or can be married with kids and a mortgage by the time they're 30.