What should I do for my 20th birthday in Seattle, WA?

I'm not into the club scene, either. But I would definitely (!) EAT in Seattle. Seattle is one of my favorite places in the world to eat because I found the food fresh, relatively inexpensive, and the chefs innovative/creative. There are fabulous restaurants there! You didn't say when your birthday is, but if weather permitted, you could go out on a sailing cruise for the sunset. Really pretty. Have fun!