Grouping clients using a DATEDIFF & TODAY( ) function

I figured it out. Power BI it required me to break it into two different items (including one that controlled for blanks or I lost customer IDs).

First, I had to create the datediff function: Days since Sale= DATEDIFF('table'[sale date], TODAY( ), day)

Then I had to put that measure into a column to break the values into groups. Once it was a column, I can use it as a column or filter by its groups:

Days since sale column = SWITCH( TRUE( ), 'table' [days since sale], > 180, "over 180 days",
     'table'[days since sale] <= 180 && 'table'[days since sale] > 0, "closed within the last 180 days",
     'table'[days since sale] = blank ( ), "hasn't closed yet")