> I have been teaching languages for years and the bottom line is the vast majority of adults don't put in the hours.

There is another important aspect: learning your second or third foreign language (or subsequent ones) is easier than the first one. I think studies or comparisons which neglect to take that into account are flawed. Adults (at least outside the US) are likely to be learning their second foreign language, not their first, hence should do relatively well, in spite of a (possible) age handicap.