You have low pop planets that are able to build PD's? What are you doing wrong? By time my planets hit society level 50 the pop is somewhere up near my home planet. I'm not bothering with building PD though except close to where I am fighting, I would rather stockpile the resources.
that's the difference between starting with tons of arcs and a couple of arcs.
with 2 arcs, my lvl ~90 is getting near max pop. obviously if you start with tons more, you'll get to max pop way earlier.
