I have just been looking at items in the Lost auction and their are several characters passports which include birthdates. I will list them.
Jack - July 14 1966 although his customers declaration says December 3 1969
Hurley - December 29 1978
Kate - August 3 1979
Michael - July 3 1963
Sayid - his passport is in Arabic so I don't know what it says but his customs declaration says April 25 1972
Should we consider these to be canon?? It seems to be a semi official source.