Yes, complicated. That is why even laws use loose language like "appears to be" and "underdeveloped" versus chronological age (e.g. when to card a consumer of alcohol or tobacco). Many games and other media, and most businesses that rely on sexual, youthful appearances play with that ambiguity between appearance and chronological age (e.g. all the "teen" porn).Thanks for that.
So I gather there's no tag that means "looks under 18 regardless of the stated character's age". Maybe "underage" would be a good one. Almost every game mentions the "all characters are over 18" phrase, because it's the most important classification to adhere to, but we don't even have a tag to denote that. Seems like an oversight.
I guess it's also complicated by what does "looks 16" vs "looks 18" mean? Any two different people may disagree.
Rule 7 determinations on this site rely on gross appearance of underdeveloped characters. It is nearly impossible to tell the age of a character in a two-dimensional story. Instead, they make a guess based on the extreme appearance of child-like versus adult-like. Subjective but "most" people would on the decisions made here.
At the risk of reigniting an ignorant argument on this thread, the dev uses this discrepancy to her advantage (and there is nothing wrong with that). Chronologically and mathematically, it is possible to determine the rough age of the characters. However, their appearance remains the same. So, perhaps they are under 18, but their appearance is the same as when they are over the age of 18. Just a thought.