Selecione suas células (data),
Use Conditional Formatting
New Rules
Use a formula to determine which cell to format
Format values where this Formula is True
write the following:
=(Today()-A1)<=120
Format Green
Repeat the above instructions and write the second formula:
=And((Today()-A1)>=121,(Today()-A1)<=180)
and Format Yellow
Repeat again the above instructions and write the third formula:
=(Today()-A1)>=181
and Format Red
A1 is the starting cell where is your date, Today() is the current Date in Excel
The cells will color automatically depending of the date written