They are known as the grass-eaters: Japan's Generation XX

A very imprecisely defined term, so how do we know that it accurately describes two thirds of men in that age range, roughly or not?

It is hard to tell whether this article is hyperbole or not. There is very little in the way of quantitative data to say. Although this bit of quantitative data caught my eye:

"About one third of the Japanese workforce is now casual or part-time"

That seems a huge number to me, and could account for some of the claimed changes in the culture.

I also found interesting the inclusion of "has a liking for deserts and foreign travel." These are indeed traits considered feminine in Japan, but not so much in the rest of the world (I learned to curb my enthusiasm for sweets when I lived in Japan).

This just seems like more of westernized / American culture making its way to Japan, more specifically "local celebrity" / "rockstar" culture. The critics are even using similar terminology; hip-hop has been calling guys like this herbs for over a decade now. From Urban Dictionary: Herb - Someone who tries too hard to be cool. An overzealous poseur.

Japan has always struck me as very strange, at turns brutally rigid, bullying, and at the same time very faddish. The article paints this behavior as a reaction to the salaryman excesses of the post war environment, where the people in their 20s and 30s are withdrawing from commitments and becoming virtual hermits.

The comments are fascinating with some likening them to Well's Eloi and others commenting on parallel behavior in Britain.