Depends on which country you're in. In the USA, you are protected by the supreme court ruling Ashcroft vs. Free Speech Coalition (2002). In Britain and other oppressive regimes, it most definitely is illegal as will soon be all forms of hate speech including the use of the word "gypsy" even when referring to gypsies, nudity including bare ankles, insults to the monarch, using "they're" when you're supposed to use "their", "writing too loudly", and referring to autumn as "fall."

I do remember that in the past that manga often went out of its way to declare that a character was over 18 even when it was clear they weren't. What happens in these cases where a character declares herself to be 18 and then involves herself in adult situations? Do they have experts say that this DRAWN image depicts someone under 18?? This isn't just an assault on the freedom of speech but an assault on the defining line between fantasy and reality.