As a kid I assumed no one knew how old these two were because they were mysterious ninjas, but it turns out Tecmo just redacted their ages in the English translation for obvious reasons. It's funny they went with this route instead of just bumping both characters up to 18 years old. I guess Tomonobu Itagaki refused to tamper with the sanctity of his precious DOA canon 
spoiler
I'm sad to report the PS2 version of DOA2 seems to be one of those early PS2 games that's interlaced to hell and back and will look like a jagged mess no matter how much you upscale it in PCSX2 
The "looks like a middle schooler" is the part that I'm not getting here, because that doesn't come across to me. I just still see a petite adult woman. If anything, I'm a bit annoyed at the way it seems people think that like, adult women all look like Lara Croft, and there's no such thing as skinny ones with small boobs and babyfaces. When like, fashion models exist. But I get y'alls argument about how she was clearly designed with that audience in mind. The games having cutscenes where she acts young isnt something Ive totally been exposed to because Ive not played them and what little I have seen that hasnt really come across. But I've described elsewhere how the upbeat genki girl archtype never read as "acts like a kid" for me either. So I'm honestly not sure still if thatd come across.
Anyway I agree with your and Ulysses take that theres something going on with Namco adding her and Honoka for horny purposes at the same time, but I have to rely on others with the idea that they read that way to y'all lmao. I would literally never notice on my own.
idk what to tell you, this reads pretty young to me. I'm not saying you can't have diverse body types in fighting games, I'm saying that this character design and her mannerisms in the context of a DOA game give off
vibes
If they wanted to add a lady with a petite build to make the cast more diverse, they could have easily done so without also making her this child-like
Yeah, I dont disagree with this part. They definitely could have done more to do that.
Luckily this weird break in my brain where I dont read that as anything but a petite and youthful adult woman in a costume only applies to animated characters lmao. Otherwise I'd be in need of professional help.
As is though, yeah, looking at her I can at least see where youre coming from. But its still not how she reads for me.