Research has shown that concept formation, abstraction, and mental flexibility decline with age, especially after age 70
Many fluid cognitive abilities, especially psychomotor ability and processing speed, peak in the third decade of life and then decline at an estimated rate of −0.02 standard deviations per year.
However, what does appear clear is that several different types of results converge on the conclusion that age-related cognitive decline begins relatively early in adulthood, and certainly before age 60 in healthy educated adults.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4015335/
https://pmc.ncbi.nlm.nih.gov/articles/PMC2683339/
That’s unmeasurable with any statistical tool with any degree of confidence. The error bars on that will completely wipe out the signal-noise ratio.
As a year over year measure, sure. The difference between 30 and 60 would be apparent though.