I’d ask one of the Norse pages, but they are all over the place about everything. Also, internet searches have not been fruitful, either. Question is: How far back in history is there evidence(written or archaeological) of people worshipping Freyja?
While you're waiting, here's an excellent series of overview posts on Norse religion by /u/Steelcan909. It doesn't directly answer your question, but may give you some context on why you're having trouble pinning down an answer.