If you want to have aging groups or buckets and display a summary listing the count in each bucket, you need to have several calculated fields. For example if you want three buckets, 0-30 days, 31-60, and 61+:
Your summary will have your key fields, and three measures: Sum(Bucket1), Sum(Bucket2), and Sum(Bucket3).
The syntax of the functions above may not be exact (I don't use dates very often), but hopefully it illustrates the concept. Let me know if you have any questions or if this works out for you.