You do need an information management policy (which is neither as difficult as it sounds, nor as time consuming as a timer job).
First off, you could take a look at this article on information management policy: https://www.dynamics101.com/sharepoint-information-management-policy/
You need to do the following:
Create a policy for your list
There should be a retention stage at the
Created date + 50 days (to represent aging)
This rention stage then triggers a workflow - which you create in SP Designer.
Now since the workflow requires to run only if the list item is "Closed", you need to add a condition in the first step of workflow.
Now coming to the scenario where
Created Date + 50 days is not the "Aging" for your list. You can then create a retention stage that is repeated every day (instead of running after 50 days) and then your workflow can validate the aging value as well (in addition to closed/open), and if both validations pass, further workflow activities are carried out. Basically your workflow will run everyday checking if the aging is 50 days and the item is closed. And for any item that matches, further activities will be executed.