This just came to me (well, it had been building up), so I had to reply. This girl, Matsui Jurina, is a kind of Super Idol and if we don't notice it now, we may never appreciate it while the going is good.
My reasons? Well it all boils down to this, she looks 16 but dances and acts 12. We ALL know this but when it is all happening right before my eyes I just find myself in uncanny land. It's like being happy watching Tom Hanks in 'Big', but for real. She dances on a level that compliments her body (teenage wise, maybe even adult) but her expressions are that of a prepubescent girl enjoying the funny music and wota antics. You can't fake something like this, you can get burned at the stake.
Yes, there are 'genius' kids who act and think beyond their age, but is Jurina one of them? Can't say for sure, but I'm enjoying seeing this 'kid' go to work. If she reaches 20, she will already have 8+ years of working experience! Mind-boggling.