Jimmy's Old Town Tavern in Reston, VA is an absolute riot on Bills Sundays. They have Buffalo memorabilia all over the walls, great wings, Blue and Molson on tap, and the staff goes nuts. They play songs on the PA and give out prizes too. I'm 22, and my friends and I go there and have a great time, but there's always tons of families there as well. I recommend Jimmy's to anyone who lives in the DC area.
How could I forget, every time the Bills score they play Shout, and someone has to run around the restaurant and high-five every single person there. If you can complete that task, they buy you a beer.