I believe the VoiceXML Properties are named maxage or grammarmaxage (no
dash).
I just tested this from the Studio app and those properties are not
passed through to nuance. But, I'm using MRCP v1
If you have MRCP v2, you can try entering these VoiceXML Properties in
the bottom of the Settings tab of the Form element.
The value is probably an integer that represents seconds. I'm not sure
which property would be used, perhaps try them both.
maxage 60
grammarmaxage 70