Date fields in Workflows' Condition Builder currently use numeric operators instead of date operators.
This is tracked under Enhancement 187987.
In order to use date operators in Workflow conditions, users can use a Saved Search for the condition.
This allows the use of date operators, and can be used in conjunction with the Condition Builder.
When both the Condition Builder / Formula and the Saved Search conditions are used, both must evaluate to TRUE for the condition to be met.