I recently bought a similar vase as Kastrup and Peter Harder agrees it is likely to be from the early 50s. Here is part of his response to me.
"It is off course always difficult to be absolutely sure, but in the Kastrup Glasværk catalogue Maj, 1954 there is a item no. 508 that is very similar to yours. The diameter is set to approx. 8,5 centimetres and the height is approx 15,0 centimetres – The catalogue does state that for the moment the items is only delivered in dark green colour, but yours could be from a later production where they have made in blue as well."
I would try contacting him.