The characters are 16 at the start of the story, and there are NSFW scenes.
For me and most people, as long as we are talking about fictional characters AND are above age of consent, everything goes, but Steam is more strict with its policies, sadly.
Anyway, there will be a most needed update of the game very soon. But it will be here on itchio, of course. PM me or send me an email if you want an itchio key, with a screenshot of your Steam library or other proof of purchase.