The game contains sensitive content better suited to an audience 16+ (following PEGI guidelines) or Mature 17+ ( following ESRB guidelines).
Here's the description in the Steam store: This game may contain content not appropriate for all ages, or may not be appropriate for viewing at work because of the following: murder, suicide, text-only descriptions of gore, blood on screen, implied nudity, sexual innuendos, coarse language, legal alcohol consumption.
I'd keep the beta testing to players who are not minors.