I don't get why, but it seems that few people here are interested in any of the same things I am. ... People just tend to talk about sports and dating and parties and clubs and stuff.It's not just you who has this problem. The experience you're relating probably sounds pretty familiar to many people around here. It's easy to forget that geeks are still the minority. In my experience so far, this won't change much as you get older. The "Jockocracy" is alive and well even after one finishes formal schooling, it just becomes a little less obvious and a little less homogeneous.
There may be some bastions of geekdom around the place and if you're lucky you'll have a few people that you can geek out with on a regular basis, but by and large it's lucky we have the Internet, hey.
Trust me kid (it feels weird that I can call an 18 year old "kid" now, but it feels right, I must be getting old), you will look back at your 18 year old self in 10 years with eyes you can't conceive of having today.
It's not about things really getting better or worse as you get older. It's more just about things getting different. It's not that youth is or should be this "idyllic" time and things just suck more as you get older. I think you'd find that many people who would self identify as geeks would not say their youth was particularly "idyllic".
You will be much wiser in 10 years. I know this is a cliché, but it's also true.
You will learn more from your failures than you will from your successes (I know, another cliché but again, very true), but make no mistake, the successes do feel better at the time. :)
You will have more responsibilities in 10 years. If there is one thing that has changed for me if I compare myself now to myself at 18, it is this. however much free time you have now, it will seem like a luxury looking back in 10 years. That's not to say that your life will necessarily turn into one big soul crushing grind or anything, but you will simply have more demands on your time. Some you will have desired and some you will not have. I now have a wife, I now have a budget to balance, bills to pay, a job to work at and so on. It's hard to say if I prefer my life now to the one I had when I was 18. Truthfully, I would say there are aspects of my life when I was 18 that I wish I still had and there are aspects of my life now that I would never give up to be 18 again.
Enjoy your youth and your current lack or responsibilities, try not to take it for granted (but you will, because we all do). Try not to take things too seriously. Some of the most interesting people I know still don't/didn't know what they wanted to do with their lives in their 30s. I might even include myself in this category actually. :P
Just keep at it, one foot in front of the other, you only really fail if you stop.