That's perfectly fine. Remember that the waist width doesn't tell the whole story. The binding insert points are on a wider section of the board. So your feet are likely sitting on at least 25cm.
With that said, I have size 10 boots and two of my three boards have a waist width under 25cm.
I prefer the width to be under 25cm because that means the sidecut is a little more aggressive which is nice for edge power and carving.