I 'assumed' nothing.
I merely mentioned LESS productive.
I agree that some middle-aged folks sure can't move like kids- but do the kids have the ambition or the work ethic to do the moving? Is it their, or their families' bread and butter, or just a stepping stone to a "better" job? I think things like that make a good employee, too- not to mention the wisdom and life experience a few more years can bring to the table.