This is all very interesting. I agree that BSG must be set in the far future and that human civilization must have started on Earth - if this indeed a show without time travel and aliens. The colonials are using the Zodiac of Ptolemy (late 2nd c. A.D.) and Messier's catalogue (late 18th c.). If space travel had been (re)invented on Kobol the Colonials would surely have come up with astronomical catalogues of their own.

Of course there are many other clues to Earth such as Classical mythology, family names, etc. But I'm not sure how consistent the producers are about their references to Earth. For instance, the Colonials use the Latin alphabet but the sacred scrolls from Kobol are written in a different script. It is also quite obvious that the line "all this has happend before..." refers to periodic wars between man and its own (bio)mechanical creations. From there everything is speculation.

I wonder whether the F5 can download into human bodies. This would explain their great antiquity and their human frailty. As purely virtual beings they could have guided humanity for a long time. But this is also just speculation. A few more months and we'll know for sure.