Grouping based on number ranges

Hi everyone,

I'm very new to powerbi and trying to muddle my way though it, if any one can help me with this it would be 

appreciated.

I have a table with the following columns,

File-Path  (this contains a string )

Accessed (This contains time and date)

Age (this is calculated from days, and is the number days from the current day that the file has been accessed)

What I would like to do is to be able to report the number of files that were Accessed within the following ranges

0-30 days

31-90 days

90-180 days

I can see how to create a grouping, but is very fixed and you can't adjust the boundries

Could someone guide me on how to do it ?

Thanks

Matt