About their ages:
I haven't read all of the Gynoid tweets yet (I did skim them), but I will keep posting translations over the next couple of days for everyone else. I do not recall their ages ever being stated or an age catching my eye, but I assume that if it's anything like their genders and relationship to each other, they probably don't have official ages.
About their undies:
I hope you people are happy, making me look up about loincloths on Wikipedia and in the dictionary...
On Hime's character sheet, it has a bullet point dedicated to her undies. It says:
Fundoshi are men's traditional loincloths. They are pretty much only worn for traditional occasions like the Naked Festival (Hadaka Matsuri) (imagine hundreds of dudes running around the street in loincloths) or swimming. The sumo wrestler version is called mawashi. (Note: There ARE female sumos, they are called 女相撲, they wear mawashi but it is over the top of a bodysuit covering their skin.) It seems like women in fiction who are things like ninjas or martial arts masters or pretending to be male have an underwear design like this and real women don't normally wear them, but an irl shop called WACOAL (ワコール) sells female Fundoshi. The Japanese version of the fundoshi page said that in the 80s, gravure models wore fundoshi and it was shocking to see their rumps, basically (fundoshi lack elastic like normal undies and show more of the rump). So, uh, I dunno. I guess if you want to be offended, think of these as undies and that gravure idols wear them. If you don't want to be offended, think of them as swimwear or traditional garb a man would wear. After all, we don't know if they're wearing the men's undies to seem Neo-Japanese or if it's because of their ambiguous gender. What if they are male? Wouldn't it be okay to see them if you can see Japanese men (including the prince when he was young, apparently), wearing them in public? This might have to be marked up as an "only in Japan" kind of thing...
I agree that the MMD modeler would want to know this information. I mean, we get to see Miku's undies all the time depending on the pose. Doesn't mean I don't want to rinse mine eyes in the holy water eyewash station after seeing them. Just sayin' what I found out. Don't send the popo after me for researching this.
About their expressions:
As for questionable facial expressions maybe they are talking about the materials for Voiceroid users that will be released on the 30th?
Admittedly, I can't really tell what some of these expressions are supposed to be conveying.