At what age do 당신 think someone should be to watch season 6?

I know the show has a lot of young viewers, but Buffy really isn't a kid-friendly show. Season 6 has the whole scene with Spike, so was just wondering because my couin has watched Buffy and 앤젤 togeter through Buffy season 5 and 앤젤 season 2, but she doesn't know when 옮기기 on. She is 11.