I adopted a 2 yr Chinese hamster just over 6 months ago. She is territorial so she will nip me if I try to interact with her, like introducing my fingers. She knows I'm her food supplier and she knows I'm not going to hurt her so I don't know what the problem is. But I pretty much just leave her alone and I see her at feeding time at night, then she's off to hiding under the bedding.
So some Chinese hamsters are reclusive and take a long time to tame. But mine will never be completely tame. I don't know what happened to her before I got her? Or if she is just a nippy hamster? So I'm providing her with a good home so that's all that matters.