I'm 21.?? My friends who watch this range from 20-22 (I don't go far outside my age group ^_^.
My baby brother watches this show (how I first heard about it).?? He's 12, and my sister's 13.
Tell you this much, college kids are totally digging this show.?? Every now and again we talk about it in class (trying to convince our professor to watch it), and just about everyone chimes in.