Hi,
The mass action system is not adapted to that.
The best would be to directly use the Joomla user manager.
There, use a filter to display only unactivated user accounts.
Then, use the sorting of the "last visit date" or "registered date" to get the latest first.
Then, increase the number of elements on the page to get all of them listed.
Then, use the main checkbox to select all the accounts at once.
Unselect the first few entries for the past 30 days, and in the actions button at the top, select "delete" and it will delete all these old blocked accounts.