Is it normal that i've never been to a party (and other things)?

Alright, so, I'm going to turn 21 in two months, and that got me thinking about the stuff I haven't done yet. I've never gone out with a guy. I've never kissed anyone that wasn't related to me. I've never been to a party at college, and I've never had a drink of alcohol, although that last one is by choice.

I was fine with all this for the longest time, but a few weeks ago it hit me how weird it all is, and now I can't stop thinking about it. The last party I went to was my own 15th birthday party, and somehow I don't think that counts.

As for the never been kissed business, let me be clear. I'm an extreme introvert. Sometimes it's so bad that I get angry if I have to be around people for longer than a few minutes. So dating and I probably aren't a great fit. Still, no one looking at me could tell that's how I feel, so something else must be preventing guys from... well, even just looking at me. I am heavier than I should be, but I've seen girls way heavier than me with boyfriends, so I don't think that's all of it. I don't care about fashion, or shopping, or braiding my hair or whatever it is girls do together. I'd rather stay home and watch tv or play left 4 dead than go anywhere, and I've had guys online tell me that's what they want, but apparently the guys where I live are totally different.

I guess what I'm wondering is this: Is it weird that I'm so far behind socially? I feel like everyone around me has been partying and dating for years, and I haven't, so now everybody knows way more than I do, and I feel... unprepared.