Kdrone -
The Data Aging report displays cumulative information about file aging on the configured file servers or SharePoint Web applications, sorted according to the last access date range. The summary table in this report lists several age intervals. By default, the bucket interval is 0 to 12 months.
The bucket is a cumulative total meaning it is the number, plus the number, plus the number, plus the number. You wish to use a larger scope and in terms of months it would be 12, 36, 60, and 72.
When configuring a report the Bucket Size (Months) - Enter the bucket interval that you want to include in the report.
What I mean is that each is added to the next before it.
When I select the range as Bucket size(Months):12,36,60,12

I get
Data (Size) Aging by last access date
Age,Size (GB),Percent,
0-12 Months,5.234152558259666,100.0, (first bucket is 12 months)
12-48 Months,0.0,0.0, (Next bucket is 12 + 36 months)
48-108 Months,0.0,0.0, (Next bucket is 48 + 60 months)
108-120 Months,0.0,0.0, (Next bucket is 108 + 12 months)
Older than 120 Months,0.0,0.0, ( last bucket is all else)
Note: Dataset in my lab is only a year old
I hope that clears up use of the buckets during configuration for you.
Rod