Here are the dates for the leaders birth/death. I'm pretty sure I got them all.
The star wars date system is just like our BC/AD system. BBY and ABY mean "Before" and "After" the Battle of Yavin. Episode I took place in 32 BBY, Episode IV took place in 0 BBY, and Episode VI took place in 4 ABY for example.
Pellaeon - Birth 57 BBY, Death: still alive
Thrawn - Birth: unknown, Death: 9 BBY
Carth Onasi - Birth: 3,994 BBY, Death: unknown
Bastila Shan - birth and death unknown
Darth Malak - Birth: unknown, Death: 3,956 BBY
Darth Nihilus - Birth: unknown, Death: 3,951 BBY
Emperor Palpatine - Birth: 82 BBY, Death: 4 ABY, spirit destroyed 11 ABY
Darth Vader - Birth: 41 BBY, Death: 4 ABY
Canderous Ordo - Birth: 4,014 BBY, Death: unknown
Grievous - Birth: unknown, Death: 19 BBY
Count Dooku - Birth: 102 BBY, Death: 19 BBY
Tikkes - Birth: unknown, Death: 19 BBY
Mon Mothma - Birth: 48 BBY, Death: 24 ABY
Princess Leia - Birth: 19 BBY, Death: still alive
Tarfful - birth and death unknown
Chewbacca - Birth: 200 BBY, Death: 25 ABY
Prince Xizor - Birth: 104 BBY, Death 3 ABY
Savan - birth and death unknown
Shimrra Jamaane - Birth: unknown, Death: 25 ABY
The One - Birth: unknown, Death: 3,956 BBY
Borsk - Birth: 31 BBY, Death: 27 ABY
Jabba the Hutt - Birth: 596 BBY, Death: 4 ABY