I believe this is done by setting the Minimum Framework Version (I'n not sure if this will completely exclude the app from the search, or if it will just show as not available). To set this when an application is generated you'd need to set the references on the desired application using this procedure. I believe that the preference you'd need to set would be the 'android-minSdkVersion'. You can find a list of many other configurations over here. After that, upload that version to google play, and it should automatically restrict new downloads. (I am not sure what happens with applications that have already been installed on a lower version that the one you set).