this is one of the most popular themes in pornography for whatever reason. incest titles increase click through rates to any porn video, even if they contain no incest content or even reference to incest
why this is so huge is fascinating. i suspect it is not really about the age gap, but rather the emotional trauma and sexual confusion so many people experience living in the same house hold as non biological "family members". the tension between "it is taboo to be attracted to my family" and "I am sexually attracted to a physically attractive person of no biological relation who lives in my house"
a male and female 19 year old of no biological relation, who only met each other 4 years earlier when their parents started dating, would very naturally feel sexual attraction to each other. indeed, they would share many of the social and biological traits of their parents. yet, this would be a massive taboo. consider the huge trauma of the mother being betrayed by her daughter sleeping with her step-sibling, or even her step-parent, fear of this, jealousy, fantasy.
of course the combination of taboo with sexual attraction will result in an entire genre of erotic fantasy much like adultery, cheating, professor-college student, or any other relationship of power and betrayal
the real question is, at what point does expressing the human condition become illegal? especially when as others have noted, it is legal to do the thing in real life but apparently not photograph it
and if this content is harmful to the consumer, why is other pornography apparently not? Should we ban also onlyfans?