Then don’t play it if it causes you to have those feelings. You’ve stated your opinion and the dev has responded stating the characters’ are of legal age. Games that pull the “don’t worry she’s 18, bro” card are often using actual children’s and teenagers models as a base for their character design, and are doing so intentionally. No characters in game are “loli”.
I don’t know if actually playing the update would make you feel differently rather than seemingly basing it off a teaser side view image but further discussion of this is going to border on being off topic as the dev has responded to your concern. If you feel anything further needs to happen feel free to reach out to an admin or mod on the matter with your concerns.