Couldn't tell for sure as I am not knowing enough about this type. Just telling you what to expect.
The fact that the item uses a Qianlong mark of this type makes it more unlikely that it is a late 19th or early 20th century, in my view. But the mark itself isn't good enough either, to be imperial. I have seen a number of doucai items on offer online, mostly in places where I would not buy a high priced item. And, they all looked pretty new.
But, I would ask for a second opinion if you already purchased this, perhaps from a first tier auction house, as they are more likely to have seen an authentic one.