Give this a shot:

SELECT DISTINCT

wcv.contact_name

,wcv.contact_organization_name

,wcv.workitem_title

,wcv.workitem_number

,wcv.workitem_created_on

,wcv.assigned_to_worker_name [Assigned To]

,datediff(d, workitem_created_on, getdate()) [Ticket Age]

FROM

contact_view cv

JOIN workitem_current_view wcv

ON cv.contact_email = wcv.contact_email

WHERE

wcv.workitem_status_lookup_value = 'Open' and

wcv.workitem_created_on > '2006-01-01 12:00:00.000'

ORDER BY

CASE WHEN wcv.assigned_to_worker_name = 'Group 1' THEN 0 ELSE 1 END ASC,

[Ticket Age] DESC

--[Assigned To] ASC