For what it's worth, this study arrived at what seems to be a more sensible conclusion.

<A HREF="http://www.jstor.org/stable/2778031">Age and Scientific Performance</A>, 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.