The devil is in the detail, perhaps. Large business class seats reflecting a desire for individual space and social rules about
closeness and what that signifies to westerners, primarily.
Large bodies, small bodies. But in societies where life and economies are predicated upon close individual ties, small seats reflect the intimacy of those transactions and concerns.

-Nancy

Your comments are far more sensible, and no doubt correct than my original glib post.

Would like to read up about physiology of different age groups though if you know of any pointers.

I don't have a medical or scientific background, but I would approach a subject like the physiology of different age groups via anthropological materials. This might be off base, but there are books like:

"The Cultural Context of Aging" by Jay Sokolowsky
"Anthropology of Aging"- M. Schweitzer

If you are in Japan, contact Jerry Eades. Though not his subject, his knowledge is encyclopedic:

http://www.ias.unu.edu/about/details.cfm/ArticleID/638/search/yes

Thanks for the pointers Nancy.