It seems to me that the demographics "requested" (gender, age, etc.) are not what is needed to design passenger space. You need characteristics like height, weight, butt size, giant hats, and so on.

Have you considered simply hiring data gatherers (of which I have read from time to time), sit them in a gate area with a clipboard, and have them tally random passengers by gender, age (child/young/middle/old), height (tall/other), weight (skinny/normal/fat), butt (tiny/normal/huge), and so on?