Also playing with the latest DW20 pack & having trouble getting an empty void age. Even with boundless sky it looks like i'm surrounded in void fog like you get at bedrock level. Even writing the age using an entire stack of paper to specify everything I still get random tendrils or spheres filling the void. If I wanted to have to mine the area before building I'd add in something worth mining. I'm hoping I just have to switch from bright to normal lighting to get my black skies to actually look black. Arrgh!
Adding 3 each village, cave, & ravine pages seems like overkill, but it got rid of the random structures. I still have brightly lit void fog instead of clear, dark skies.