I think most people younger than 40 have at least some knowledge of 3D Printing. Very minimal perhaps, but they at least know that 3D printers exist. I'd say only about 2% of the population know a good amount about 3D printing, like how it works, etc
I'm not really sure I would agree with this. I would probably guess about 45% of people under 40 know that 3D printing exists. However I doubt they know how it works, or very many details about it.
James