Inventory Aging is a rather innocuous looking member of the band of (now) seven metrics that, under the Volcker rule, banking entities with significant trading assets and liabilities are required to calculate daily and report monthly.
As written, the metric description seems straightforward enough:
Inventory Aging generally describes a schedule of the trading desk’s aggregate assets and liabilities and the amount of time that those assets and liabilities have been held. [It] should measure the age profile of the trading desk’s assets and liabilities and must include two schedules, an asset- aging schedule and a liability-aging schedule.
The graphic below broadly outlines the processes of asset/liability tagging, matching, sorting and netting of trades involved in generating an inventory aging schedule.