I think the trap here is that productivity entails the exchange of hard currency. In some societies activities like childcare, household work, shopping, gardening, etc. are uncompensated labor often done by seniors. Historically, they have also been conduits for preserving knowledge and educating new generations. But things are changing. Seniors' productivity as a cohort today will probably diminish with increasing lifespans, decreasing healthspans, and being a larger proportion of society than has historically been the case.