Are you just trying to determine if each person's 'first start date' is more than 6 months ago?
How do you calculate the 6 months - is it 'to - the - day'?
You can research the 'DateSerial()' function to use in your query.
For instance, I use this in the Criteria row of a Date field in one of my queries:
Code:
Between DateSerial(Year(Date()),Month(Date())-13,1) And DateSerial(Year(Date()),Month(Date())-12,0)
It gives me data for the entire month that is 13 months ago [Eg: in June this year -> I get May last year's data].
Hope this helps!!