Dating in the dark rickard
The Northerners, descended from the First Men who were never conquered by the Andals, have a decidedly negative view of the Andal invasions.
Still, all legends and oral histories may have some kernel of truth behind them. Martin himself, is that as the saying goes, history tends to be written by the victors.
Other characters are older (Eddard Stark and Robert Baratheon are ten years older than their book counterparts) or younger (Ser Vardis Egen is decades younger than in the book, while Theon is two years younger), though for the most part this has no bearing on the timeline.
In the book chronology, roughly two years pass between the beginning of A Game of Thrones and the end of the third novel, A Storm of Swords.
The earliest written histories date back to about 6,000 years ago, when the Andals first introduced writing to Westeros.
The First Men had no writing system more advanced than runes for marking graves, thus all history before 6,000 years ago relies on oral tradition.