I've had this problem with my own story, I don't like heavy magical worlds my worlds are more like Tolkiens, long drawn out with few very powerful magical entities. But finding help with pre-medieval demographics and lifestyles are much harder because so many fantasy are commonly medieval in sense.

My current story I am trying to work out involves a post-neolithic hunter/gather tribe as the first people to enter a land between 2 large mountain ranges. I wonder how they would culturally and demographically develop by themselves culturally and demographically before more groups are introduced in my story. I want to spread them out over the valley over a few decades to maybe a couple centruries and create cultural tension between themselves as they prosper economically and agriculturally while creating a social system beyond a nomadic life.