Not that rare, but not too often either. You will see even less in crowded, more organized place such as central tokyo.
Most people still prefer commuter in that country. Besides since the kind of bike they can LEGALLY obtain a license at that age is...
Freaking FIFTY CUBIC Moped.
The 'impressive' and 'badass' part is certainly out, you see them often in rural areas though, where it's convenient due to absence of public transportation.