Janice Dickinson is too old and too broke to repay the huge debt she allegedly racked up by bouncing checks, but luckily she has a rich fiancé -- this according to the bank that just settled up with her.

According to bankruptcy docs, City National Bank claims Dickinson owes more than $300k in connection with checking overdrafts ... but the bank just agreed to end the whole matter for a mere $100,000.

In the docs, the bank takes a serious cheap shot at 59-year-old Janice, saying, it will be tough to collect the money from her "due to debtor's age, lack of assets and lack of income."

The bank also claims in the docs ... Methuselah Janice can't swing the payment plan they've set up -- $10k now and the rest over 3 years -- so, her fiancé is gonna pony up the initial amounts.

Cold-blooded.