The world age can start at year 2, and end at year 1050. That is before you start playing on it.
If you create a young world, at year 2, for example, the game will not generate data for their parents, their sons, daughters and stuff. Not just yet.
It might be affected by "Cull Unimportant Historical Figures" or something on World Creation.
Basically, as you start playing, they start making friends, enemies, marrying, making children and so on. That is procedurally generated on world creation automatically, but if you play on adventure mode, I dont think the game keeps procedurally generating history like it would in world creation. If you play Dwarf Fortress, then I think it does, the world evolves, everything changes and so on.
So a good idea, is to start in an old world, where everybody has its genealogic tree, who they met, who they killed, what they did, what group they were part of, who they married, who were their children, etc.
But, you can also start in a young world, with just 2 years. at this point civilizations are just starting to flourish, and as you play Dwarf Fortress mode, after many years (like 200 or so playing hours through one or multiple different fortresses) eventually civilizations will reach each other boarders and start their socialization. I generated many worlds with the same settings but distinctions in the age, and I noticed that civilization will grow steadily and at around year 25-50 their territories should start encompassing each others. At around year 100, I got many conflicts going on.
At year 1050, you run the risk of having multiple races extincted, thats why I prefer to start in worlds with just 2-25 years, unless thats what you want.