This is not an accurate summary of what the study actually found. The article proposes a high-level explanation for how one aspect of learning changes with age.

This is not an accurate summary of what the study actually found. The article proposes a high-level explanation for how one aspect of learning changes with age. The actual cause of this high-level change could be lower-level age-induced differences in neurotransmitter levels or in neuronal function and connectivity. As the article's summary points out, the actual biological basis needs to be investigated in further research. It's also important to note that this study found a plausible explanation for changes in learning performance under specific circumstances. This is a very important qualification. Learning in general is believed to involve many different interrelated mechanisms. It's well established that many different cognitive abilities (perhaps most importantly working memory) diminish with age, and some of this degradation is likely related to natural cerebral shrinkage (a healthy 75-year-old has a 15% smaller brain than a 25-year-old).