I suggest using average standard rather then extreme possibility. Can 18 year look like that ? Sure can because the genetic variance is huge. There is the whole fucking barely legal baby face shit after all. But they are not popular because they look like adult woman, they are popular because they are adults that look underage.This calls for self inspection.
Regarding my comment, it's literally what Scamlius posted; it's Gelato but not really, as the original concept was indeed a loli (some nonsense about her being a replacement for couples who lost their young daughters iirc), conceived to reap that sweet lolicon $upport... and it worked quite well, bumping the patreon numbers; with the same amount of backlash when he didn't deliver. Now it's like the other two guys also pointed out, more of a young adult. I second their opinion, if you think adult women need to be 170cm tall and have huge proportions, consider self inspection.
According to Jung, the things that bother us most about other people are often projections of our unresolved issues, fears, and insecurities.
I'm confident that if you ask average person on the street in the west Alet would already be questionable adult and Galatea would easily be marked as underage.