Aged receivables report is not concerned about individual invoices. You should open Customer statements report which is what your customer should receive as it contains all relevant information.
It’s standard in accounting to use days for aged receivables, aged payables, inventory turn, and many more things. It would not be good practice to wait months to take action on things.
The thing is, a receivables report organized by literal months does not convey useful information on delinquency. I’ve never seen decisions based on who was due in February or March, but rather how many days overdue payment was.