A couple of thoughts about this. First, I agree, 16 is too young to be "writhing" on stage. While I'm sure Miley would like to shed the "tween" status she has, she's just not going to have broad appeal to adults over 30 at her age. She shouldn't be so quick to grow up. Shame on her dad, Billy, for allowing her to do the things she does.
All of that said, I love this song. Were she 18 or 21, it would be a great performance. As it is, it makes me a bit uncomfortable. Still, if she's trying for a more mature sound, this song is it.