the overlap between two generation's cognitive prime age is narrow That argument fails on the above point - you picture generations as discontinuous (or nearly

the overlap between two generation's cognitive prime age is narrow That argument fails on the above point - you picture generations as discontinuous (or nearly so), whereas in the normal, non-technical sense - as here - they are simply a useful picture of an aggregation over a continuum of ages in the population as a whole. Working and academic environments - beyond a certain level of competence - are populated by individuals of varying ages and experience which are more likely to be demarked by managerial levels and career choices than individual knowledge and aptitude.