I've played twice now about thirteen years of the game. It feels like my people are doing OK -- I can keep them at 4+ stars and 4+ hearts and they seem to start the game pregnant, so babies come up at first. But then, after a while; certainly by year 10, no more babies are born and the villagers have started dying of old age and my population crashes down below 18 or so which feels like a tipping-point after which I can't generate all the stuff I need to -- not enough people to both mine iron and make tools, and I have to start giving up nutritional variety, etc.
And it feels like there aren't really that many more knobs to twiddle. I'm pretty patient with games, trying again and again with different strategies; I just don't see what I might do differently.
So, are there factors that go into reproduction that I'm missing?