Advanced age and low income are not included in the list of exclusions and exceptions. Unless one of the listed exclusions or exceptions applies, your father's canceled credit card debt will be taxable. However, depending on the amount of Social Security income (or any other income) and the amount of canceled debt, your father might not actually owe any tax, or the tax might be very little (or he might not even have to file a tax return, as macuser_22 suggested). You could do a what-if tax return with his actual Social Security income and vary the amount of canceled debt to see how high it can go before any tax is incurred.
