Large parties with a bunch of strangers aren't the only form of social situation. When I was in college, I had a mostly regular group of friends that I'd hang around with and chat politics/philosophy/whatever till late in the might. Regularly to 2 AM, sometimes to 4 AM. These days, I spend most of my evenings alone and naturally go to sleep around 12:30 to 1:00 AM if left to my own devices. I'm definitely more of a night-owl and an introvert, but close proximity to friends, as I had in college, I would stay up real late.