Hi Manny, and welcome to the forum.
There are probably a few ways to handle this; here's one.
First, you need an "as of" date to determine how old your invoices are. You may be able to capture this from the report itself, or you might want to use a runtime parameter calculated field.
Next, build a numeric DaysOld field, with this expression:
The expression for your Current amount would be:
The 31-60 field would be:
Other aging buckets would be the same, until your last one. If it's 360 days +, then the formula would be:
Does that get the result you want?