Drop tables where the last update is over 1 week ago
All the metadata about tables are stored in the db named information_schema.

Try this:

SELECT
    TABLE_NAME
FROM
    information_schema.TABLES
WHERE 
    UPDATE_TIME &lt; (NOW()-INTERVAL 1 WEEK)


UPDATE: i forgot to mention this will get you all the tables that you need to drop, after that you can build the DROP statements.