Just to reiterate - many factories made these decanters into the 20th century, not just Holmegaard. And so that Holmegaard didn't make this would not automatically confer antiquity.
The clarity of the glass, in the images, looks firmly 20th century. In some of the photos the glass has a bright blue-ish tint when it catches the light - this would probably place it at mid-century, at least.