Some of the kids helped me do the squash for the drinks at club last night and it crossed my mind that squash strength would be a good guide if you were trying to guess their age. The exact system would have to be worked out, of course, but the basic guide would be that the sweeter the taste the younger the maker. One problem might be that some old ladies seem to revert to childhood on this front. A good general guide though, I'm sure.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.