Stenocactus vaupelianus

Perfect ball. Does it stay "ball like" in later stage?

I believe it stays very much ball shaped. It doesn't grow very big - eventually about 12 cms across, so I've read.
I've had it about 4 (?) years ...
It should flower, but hasn't done so yet ...

Hope it will flower soon. In the desert the cactuses usually bloom in the spring. I wonder if it is also true in "captivity".

It depends on the species. Some flower in spring and some later on. The same ones flower at the same time every year, but there are more spring flowering species than later ones.