I wonder how much of the adult language learning research is like the research on physical fitness. There's decades of research about the precipitous decline in fitness and strength that comes with age. More recent research shows that the decline had more to do with decades of an increasingly sedentary lifestyle than physical decline. Yes, a fit 60 year old is less fit than a fit 30 year old, but still may be quite fit. Probably the decline in ability to learn languages is real but may not be nearly as pronounced as some studies show.