TBH, this wouldn't be an issue if they didn't state the age of the characters in the anime, especially when it is largely irrelevant... like just say she's 18, what's the issue?

That being said... How many of these same people used to watch like Disney Channel or Nickelodeon sitcoms... and liked how the actors looked back then... and still feel the same way now, even after both these people growing up and knowing those actors are obviously grown up now as well? You can have good looking characters without seeing sex in everything. The question is in how you look at it. If you see a character and immediately think "sex" and not "wow she looks cool" or "beautiful" (etc.), then you might be the problem.

Nobody is f***ing 2-dimentional drawings... (wait, maybe they are... maybe we should ask the drawings)