Hate to break your stride again, Crow, and I am sure that Slavic languages are old, but what about Greek, Latin, Basque, primitive Irish, West Germanic languages? They all have written accounts that precede the first Slavic written account by hundreds of years, if not thousand years.
i read somewhere that polish and chech begun to separate in XIII
True, like the Germanic languages the Slavic languages are derived from the same "mother language" with slight variations due to geographic locations.
However, I read somewhere that Polish uses grammar that comes closest to the ancient Slavic mother language.
M-G (Slovene, for example has its first written account in 972 while Basque has its first in 300)