Go Setup>>Products.

 Click on manage categories link.

 Use the filters to find the category for which you want to setup the max days. Go to the Actions column and click on Edit.

Go to the Hide from Inventory after field and enter the number of days after which the system should hide products of this category from the On Hand inventory once they reach the age set up. Leaving the field empty, the max age by default will be 180 days. Users will be always able to find the products filtering by a date range greater than 180 days. In the site, the system will also take into account the Max-Age configured as a global setting or the ones set per category or specific item.