The abstract has these two statements: > ”Cross-sectional age-skill profiles suggest that cognitive skills start declining by age 30 if not earlier.” and > ”

The abstract has these two statements: > ”Cross-sectional age-skill profiles suggest that cognitive skills start declining by age 30 if not earlier.” and > ”Two main results emerge. First, average skills increase strongly into the forties before decreasing slightly in literacy and more strongly in numeracy” Does this mean that this study contradicts the popular common understanding that cognitive skills decline after 30? Or am I missing something? For me, personally, if feels a more impactful finding than the “use it or lose it” one