What would do at 23yrs in this situation?

People tend to associate 'partying' as having a good time and doing that particular thing so that you won't 'miss out'. You're not missing anything, dude. It's just something you're interested in. And you don't have to necessarily party just because many others are. If you don't want to miss out, just make sure you're not stuck at home all the time. Go see a movie, even if it's by yourself. Go try new dishes at restaurants. Go to the state fair when it comes around, go see a play, etc.

As far as your shell, I would suggest try taking some lessons or classes on communication, leadership, and public speaking. If you want to break out of your shell you need literally, confront your fears. That's the only way to conquer them. I'm take a leadership course right now and I've always had social anxiety for years. But now that I'm being forced to speak to people, I'm noticing a difference. Practice, practice practice makes perfect.

Also the reason you're in a shell in the first place is because you don't have enough confidence within yourself. You also think too highly of others whereas if you didn't, you wouldn't care how so much about how to perfectly present yourself to people. They are not gods, they are human just like you. They don't deserve so much of your energy being shifted into fear.

I think you should join social groups