Yeah, I was probably about 9-ish. I caught seasons 6 and 7 during its original airings on the UPN network. The only episode I ever missed was "Dirty Girls". I was hanging outside with a friend (which was rare at that time), and I remember saying, "gosh, I should get home, I'm going to miss Buffy", and he was like "are you seriously going to ditch me, after all the fun we're having, to go watch Buffy?" And then I couldn't leave after that. Haha. 😛
To be honest, I couldn't tell you which age you should start watching the show, because Buffy didn't make me some sort of violent person or anything. If anything, it made me a hermit, because all I did during my junior and high school years was come home from school and watch Buffy all night. 😀
No seriously, even though the show has its dark moments, Buffy (and her gang) are great role models. The stories are timeless, and there are valuable lessons to be learned through the show. It should be required viewing for anybody, at any age.