We know that Alleria and Turalyon were in the nether for 1000 years they left their son when he was an infant he was born shortly after the Second War (Year 7), he would be around 19 years old during the events of the Burning Crusade add 10 years he is now 29. So 29 years ago his parents were trapped along with the others after closing the dark portal and went missing after 3 years on draenor meaning they haven't been seen for 26 years minus a year (maybe ) of joining the army of the light, they have been trapped in the twisting nether for 25 years of our world so 1000/25=40
A year on Azeroth equals 40 years in the nether, Illidan is been dead for a decade so 10x40=400
There you go Illidan has been running for his life 4 centuries now