Tracking Age Of Inventory In Warehouse FIFO Accounting

I am trying to create a worksheet that tracks the age o f the inventory in my warehouse. I am charged each week at an increasing rate and want to be able to track what these charges will be. I would like to be able to sum up the data below in a pivot table that shows how many units are falling into each age group, this would add up to a max o f 10 weeks o f increasing charges.

3/1/14 received 1000 units
3/6/14 ship 600 units
3/8/14 charge for 1 week at 400 units
3/8/14 receive 500 units (900 pieces on units)
3/13/14 ship 300 units
3/15/14 charged for 100 units at 2 weeks and 500 units at 1 week

This needs to be able to assume this is going on for 10 different items, I would like to be able to track the items independently and in bulk.