Never let an item of inventory have a birthday in your business.
This is excellent advice. It is easy to track and easy to manage.
I did some work for a newsagent last year and in stationery alone they had $37,000 worth of inventory items that had not sold in six months and $13,000 of items that had not sold in over a year. That is, not any of the stock of any of the items had sold in the period.
Acting on this starts with tracking it. It is dead set easy. Track it. Identify the dead stock. Quit it. Don’t replace it.
Dead stock is an opportunity cost to the business. It weighs you down and causes you to offer a sub-par shopping experience.