To setup the beginning balance for AP/AR Aging process, for entities, we have to post the opening balances for Customers and Vendors. In NetSuite, it is possible to use the ‘Opening Balance’ field in the entity record.
At the creation of a customer or vendor, the opening balance, opening balance date, and opening balance accounts fields are available under Financial tab.
If we enter an amount in the opening balance field, the system automatically creates an opening balance Journal Entry for this amount with the specified account. If no account is specified, NetSuite picks the last used AR/AP account.
These fields are only available at the time of customer or vendor creation. Once, the record is saved, these fields will not be available in the form. So no customizations can be done on these fields.