Hi Danny,
Frank is right, LastSold is not valid, as it's not always correctly updated by the system.
What about using [Transaction].[Time] in the [Transaction] field? Make an SQL query that will list You (and order by) the last date of a transaction for each SKU You have in the database. Like SKU 1 was last sold on that date, SKU 2 on other... and order them by this date. In the same query You can get the SKU, ItemID (from TransactionEntry table) and the Transaction.Time. From there filter the ones with Transaction.Time before Today minus 5 years (or the time You want). From there, You can update only the Items with ItemID's in that query, putting them inactive...
Hope this make sense...
Kind regards, A.