Bohdan Andrejewicz Sakowicz - bohdan sakowicz birth date?

All the sources of information that I have read list date of 1440 c. Vikorija Ruskuliene, who has done extensive research, (and well done I might add) has entered his birth date as c. 1455, and has changed it from, 1450. The year 1455 would make him a little young to have accomplished what he did. It would make him only 19 years when Elzbieta was born. He also would have been 19 years old when he became viceroy of Braclawskiego? Anyone have any information???