The whole article hinges on an empty premise: "Possible explanations could include changes in brain plasticity, lifestyle changes related to entering the workfo

The whole article hinges on an empty premise: "Possible explanations could include changes in brain plasticity, lifestyle changes related to entering the workforce or college or an unwillingness to learn new things — potentially while looking foolish in the process — that mounts with age." I would argue (as a European) having learned 7 languages over the years (only 2-3 to any practical level, but including Greek and Latin as a firm foundation) only time matters. Invest the time and you can go to a pretty decent level in any language. Some are harder than others, fluency takes periods of continuous exposure, but it's all a function of time spent. Kids not only have time and emerse themselves by nature in their first language, but are obliged via social structures to practice (schools even come with punishment you know). The rest might give you some hindrance at 20+ but nowhere near the effect of don't spending the hours reading and talking.