The reason for age was simple - as you grow up there are more dependencies which demand a share of your time and more responsibilities to live up to - which is what pulls you down. The age question was not about productivity. Given equal circumstances and responsibilities, there is no question that this thesis would hold true - however that is not the case !!

Sorry Marc - this time it was thought through a little tooooo much and the original reasons that started this debate were largely ignored. I hope you read this comment.