^ ^ Natsume is 11 right now. In her intro you can hear her say she was 10 at the time. The event took place July 17 2016, 3 day before her 11th birthday. So that would make her birthday July 17 2005 which is still younger then Ichigo' who was born July 15 2005.
^ If Riai was born between April1 and July 14 2005 then the info is correct. She was 4th grade at the juni event which took place in March 2016 meaning she was 9-10 during that school year (April 2015- Mar 2016). So the birth dates of the 3 youngest girls are as follows.
Matsunaga- Between April 1 and July 14 2005 Yamada- July 15 2005 Nakayama- July 20 2005
Riai just closed her blog and made the KSS annoucement. Some more info I managed to grab before it was closed. Her favourite colour is yellow. She one older brother and one younger sister. Her sister Nanoa (なのあ) is also a model.