Individual episodes are generally not as rewarding if you don't follow the storyline.
The demographic is 6-11, but it's a consistently high ratings performer even outside that.
The question of 'how old are you' was asked on the imdb.com forums for this show and there was a surprising amount of 20's, 30's and 40's. Also, I'm 18 if you're wondering. My friend who recommended it to me is 20.
It's also very quotable. "There was this boobytrap and... well, uh, we boobied right into it?"