We have a former employee who retired from service (fifteen) 15 years ago but has an unsettled disallowance. Can the receivable from this retired employee be written-off from the books since its collectability could no longer be ascertained.

No, Section 4.0 of COA Circular No. 2016-005 dated December 19, 2016 provides clearly that receivables arising from disallowances and charges cannot be a subject of a write-off since it is not one of the legal grounds for extinguishing an obligation under the law.