Maybe everyone just had incredibly boring, uneventful lives up until the time they turned twenty; so boring in fact that it's all a blur and there's no point in even thinking about it.
Seriously though, I think very basic knowledge about the area you spawned into (growing food, chopping wood, using a harvester or an oven, etc.) should be a given, but there should be no specific information about your character's past experiences, likes and dislikes, etc. that might predispose them to anything.
All of my characters are still pretty new, but I find it interesting how they've gradually developed personalities based on where they started out, with no conscious steering from me.
One is in a large, sheltered city with plenty of food, and early in life she heard rumors about how dangerous the surrounding areas were, so she's become kind of a timid, stay-at-home girl with no desire to leave, something that's reflected in the job she just got. Another is the exact opposite, in a place with no food where several people have actually starved to death, so so she has more of an aggressive personality and is much more connected to the community. Yet another started off in a town with way too many rules and regulations, so she developed an independent streak, taking off as soon as she grew a little food and by luck stumbling across another place that shared her views and starting up a career as a trader. And so on and so on with the others.
None of them necessarily have really dramatic personalities that stand out too much, but to me at least it's amazing how different they are, even if not too long ago they were all blank slates. This is why I'm addicted to Cantr.
