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 
I gotta say, I'm not really a fan of the idea of deciding characters "look" like adults and therefore shouldn't be children in the story. Sure, these characters could be 25, or they could also be 15. 15 year olds can look pretty much like adults, and it isn't their appearance which determines whether they should be treated as such. It's their maturity and life experience, the invisible development of the brain, which matters.
The way I see it, there's really no such thing as a character "looking like" an adult. Did you not know any tall bearded kids in high school?
If its story relevant, sure, but it isnt here is the point. Also like I'm sorry but in this case I have never seen a 16 year old that looks like Kasumi in my life.
i went to school with a dude who at 14 looked more like
than any kind of teenager. tbh he looked older and was balding more.
it definitely happens
Idk I've worked with kids and I've seen girls "overdevelop early" and they still look like kids to me? Ive definitely seen girls 15-17 who can pass for adults with like makeup and in posed photos but the game gets given away in how they behave almost always. Maybe like if its a professional child actress around that age playing a part consistently and you never see them out of the role lol. But even then though like, they dont look like THIS
Kasumi to me is a definitively 20+ looking character and cannot pass for younger regardless of her canon age. I have never seen a child that looks like that and again, I've worked in childcare a lot.
Boys though yeah I guess. I mean Ive never seen that but I can imagine it I suppose.
To be clear, I obviously agree that real children who pass as older should not be sexualized, thats not in question here. I just think that animated media that creates characters that look fairly definitively 20+ but have canon ages of 15-17 are doing something extremely weird that I don't understand and seems unnecessary. Especially if the character is sexualized. Unless there's like a specific story relevance to their age it seems purposeless and uncomfortable.
Jotaro's almost too absurd for me to have that reaction too because its just silly lmao.
I'm not really sure what I'm looking at. They don't look like mid-poly video game models? They don't look like Asian girls in makeup? I don't understand what feature you're trying to point out that marks this character as definitely an adult.
Yeah idk how to communicate this any better. She looks like the polyogonal video game version of an adult woman to me. I really cant be any more specific than that.
Right, but that's what I'm asking. Why does this read only as an adult to you? Because it doesn't to me. It reads as someone who could be pretty much anywhere between 15 and 30. What feature are you looking at which you don't think could be present in a depiction of a teenager?