Days Overdue Field in Customer Record and the Age of the Customer's Oldest Invoice are Different

The Days Overdue field on the customer record always age receivables based on the transaction's Due Date while the A/R Aging Report ages receivables based on how the Aging Reports Use preference is set.

Navigate to Setup > Accounting > Accounting Preferences > General tab > Aging Reports Use.

Transaction Date option computes the age of the invoice from its transaction date. This preference will result in different invoice age calculation in your AR Aging Report vs Days Overdue.

Due Date option computes the age of the invoice from due date. Using this preference will calculate your AR Aging Report Age the same as Days Overdue.