They're all 16 now, these girls...
But the funny thing here is that... not a single one of them has anything resembling a figure at all. If they hadn't got taller (besides Hitomi), you wouldn't even know they were halfway through puberty at all. Honestly, I can't remember if any of the ADULT women in this series have progressed beyond burdock root level. Pretty much the only way to distinguish between the girls and the guys is that the girls wear skirts (and some of the guys have stubble).