In my case I failed to use Group Stats plugin (2.0.30) with QGIS 2.14.11 and 2.18.3 on windows64. Tested on several datasets: points, polygons, and csv.- But I am not sure what I have missed.
I want to click on this Calculate button.
You would need to specify on what value the 'min' function should run.
Also taking a look at this tutorial might be of help - Group Stats tutorial