bedroom tax in UC housing costs and mixed age couples

Are mixed-age couples exempt from the bedroom tax in UC.  I had thought not but quick benefits calculator programme won’t let it be applied in the case I am dealing with.  Any thoughts?

Update:

I have just installed the latest version of QB calculator and it is now letting me apply the bedroom tax in this case.  For some reason the old version (up to 31/01/19) wouldnt allow this.  Anyway, this seems to confirm that mixed age couples are not exempt from the bedroom tax.