Those assets only produce income because of the current working population. This isn't strictly required of course, but it has been the case for a long time and is likely to remain mostly true for the foreseeable future.
This is some strange, broad descriptive logic that makes me think you just want to give credit to the working population for retirees. You could make similar claims about consumers or infrastructure being required for assets to make income, or any other facet of an economy.
