Hello Vishal,
1) Can I get reference document / Inbound ID for In Hand Stock?
Ans : I assume that you should be able to get this details.
Inventory Ageing data source does not have the details about the source document. But you can join two or more data source and get all the details in one report using joined/Combined data source.
You can check data source : FININVU01 / Report : FININVU01_Q0001 (Material Inventories - Line Items).
Line item data source will have the source document ID details and inventory aging will have the aging details.
Not sure whether this will work and suffice your need or not.
So Basically, Now if you need aging as well as source document in the same report, you will need to create new joined or combined data source, Design the report based on the newly created data source.
2) Currently its showing all product Inventory Age (In Days) 734746- (which means /365 as year = 2013) Data should show accurate figures.
- I did not understand the query.
Since I am no expert in this area (reports as well as logistics). Can you please provide some more details, may be I can check then. 
Regards,
Harshal