Dynamic Stock Aging

Hi,

I am trying to get a DAX formula that can give me stock aging through time. For exemple, if I go back to February, I can see my stock aging at the end of the month. 

For now, all I could come up with is an aging as of today, see formulas below. How can I make it dynamic ?

0-30 days = SUMX(FILTER(INVENTAIRES; max(INVENTAIRES[Posting_Date]) && max(INVENTAIRES[Posting_Date])-30); INVENTAIRES[Sum_Remaining_Quantity])

30-60 days = SUMX(FILTER(INVENTAIRES; INVENTAIRES[Posting_Date]<=TODAY()-30 && INVENTAIRES[Posting_Date]>TODAY()-60);INVENTAIRES[Sum_Remaining_Quantity])

Regards,