User blog comment:Jopjopjop/Volume 19 Quotes / Spoilers/@comment-101.175.204.97-20141104093453/@comment-24468758-20141104185951

Koneko's built is that of a little girl nowhere near her age:

"That’s the girl from 1st year, Toujou Koneko-chan!

She’s from 1st year, but she looks like an elementary student because of her childish face and small body!" Vol 1, Life 1, Part 8



But as I already said you are right that her behaviour hints at an age befitting her appearance.