Hi Naveen,
You are having posting date ..say 01-Oct-2014 and you need to used variable 0DAT(Which is calday..i.e Today)..And the difference between that will give you the Age of the Material. 01012015-01102104 ...here in this case its aprox 90 Days..We need to use Formula Var to find the difference for dates.
rgds
SVU