Weird indeed. So I'll confirm, that in reality Einari is only 20+ game days old character?
Upon the load his data indeed tells he's lived 499 days.
I've got absolutely no idea what's the case here. In theory it could be a result of some variables overflowing, and then corrupting the day counter.
But why, that's the mystery.
Did you go about with similar playstyle with all the characters that ended up in the day skip?
Also mention is there was any modding, or third-party stuff which might affect to game values.