Aruna,
Yes that is true, as on the standard SAP ByDesign Aging receivables report there is no credit limit on it. So therefore you will have to create a new report from the existing report adding credit limit to it.
Go help Business Analytics-->Design and assign reports--> highlight aging receivables-->report as copy-->add new name--> Next--> Next--> find where credit limit is and select it--> save and assign the new report to receivable work center(This will take time so consult help center).
If you need help go to Help center and read Create financial reports.
Hope this helps.
Regards,
Emeka