The loan itself would not be set up in AP-B but rather in GL-B as a cash receipt, debit to cash (you got money) and credit to loan payable.  Then as you make payments, you process in AP-B posting the debit to the loan balance and interest as applicable and the payment credits cash.  The balance sheet will reflect the loan paydown, not the AP Aging.
 
AP-B "Beginning Balance" is for entering open AP balances when implementing a new installation.