For what it's worth, this study arrived at what seems to be a more sensible conclusion.
Age and Scientific Performance, Stephen Cole (1979).
The long-standing belief that age is negatively associated with scientific productivity and creativity is shown to be based upon incorrect analysis of data. Analysis of data from a cross-section of academic scientists in six different fields indicates that age has a slight curvilinear relationship with both quality and quantity of scientific output. These results are supported by an analysis of a cohort of mathematicians who received their Ph.D.'s between 1947 and 1950. There was no decline in the quality of work produced by these mathematicians as they progressed through their careers.