Yeah, the Scoobies acted a bit older than they were supposed to be, Dawn acted a bit younger than she was supposed to be. When re-watching season five, I was thinking "okay, she's twelve" until a reference was made to her being fourteen. Then again, a lot of "youngest" children are a bit less mature, so that could be it.

I was in middle school when Buffy first came on, so a bit young for it, though a lot of people my age still watched it. Mostly I just don't think it was my kind of show back then.

In a way, I think Joss was also trying to play with the whole Cousin Oliver thing, the way high school!Buffy played with teen horror. Podcasts have pointed out similarities to Freddie Krueger. (I don't watch horror, so I can't comment either way.) Unfortunately, I think that rubbed a lot of fans the wrong way.