I don't think I need anymore proof than that. They got in trouble, then had a two year time skip where everyone became legal to cover their ass as you said and not have another game banned somewhere. They had the idea for Marie Rose, made her 18 to cover their ass. Is there a specific interview where Hayashi explicitly said "we made this very young looking character 18 so an issue like Sweden won't come up again"? Probably not because that would be pretty stupid to come right out and say.
In that culture it seems they consider younger people than westerners do to be fit for adult situations. Bravely Default changed the ages of their main characters from 15 to 18 in western releases for this reason.
Except that's not proof in the least. Not all shows changes the ages of the dubious of age characters and neither does games either. By trying to use that as some level of proof you seriously have nothing except for the simple Take That of her design, not the intent of making a child character and lie and say they are 18.
If you was so right, then why ISN'T Marie Rose 16 or 12 in Japan? As you just stated, Other shows and games sometimes do change the ages of the character and it isn't like Sweden is some grand gaming area anyway so they can easily just not release there to begin with and still keep the Take That nature overall.
In other DOA titles, we already knew Kasumi, Ayane, Kokoro and Eliot was not 18 in the least, but they still added N/A and didn't change it only until after Sweden's incident in general. Just don't bother to release there(most games honestly don't, most people just import from other areas in Europe anyways.) and they are golden.
So no, that's not solid proof and I'm honestly getting tired of doing this song and dance because I have a feeling I'm gonna get warned if this continues.
Good day.