User Interface that is easy to imagine as a physical object is easier to figure out. It doesn't matter if the user is familiar with the physical object being emulated on the screen. Because laws of physics are still applicable even if you haven't seen such a physical object in real life.
The human mind is always building models in our minds, based on observations of how things look and work, and then using those models to predict behaviors of things that we are yet to explore. For this to work well, appearance has to imply behavior. Instead of starting with a clean slate each time it would be helpful if we can leverage the mental models we have already built of the physical world. This is where skeuomorphism is helpful.
I don’t have any data to back it up but I doubt that. Schools are still mostly using paper text books. And I reckon school libraries are still the main source of books for kids (who typically don’t have money to buy books). Family members who want to buy you a book as a gift, will do that on paper as gifting ebooks is trickier and less personal.
To be honest, I would bet that the if younger demographics are reading less paper books it’s because they’re reading less generally rather than switching to digital.
The human mind is always building models in our minds, based on observations of how things look and work, and then using those models to predict behaviors of things that we are yet to explore. For this to work well, appearance has to imply behavior. Instead of starting with a clean slate each time it would be helpful if we can leverage the mental models we have already built of the physical world. This is where skeuomorphism is helpful.