AnswerThey're just as old as the the Space Marines because 40k stated with Space Marines vs Orks.
Yes If you find the answer insufficient, please elaborate your question.
you take the role of space marines (a superhuman genetic warrior and fight chaos daemons and chaos space marines and orks i dont know the storyline but thats what happens
Technically you can play any army against any army, and any army with any army, except where rules specifically state that you may not (E.g. Black Templars may never ally with an army containing pyschers) It would however be extremely unusual, but so long as you have a good background story, it should be fine.
Dawn of War featured the Space Marine, Chaos Space Marine. Orks and Eldar Armies. Follow Up Expansions Featured the Imperial Gaurd, Tau, Necrons and Dark Eldar. Dawn of War II Features the Space Marines, Orks, Eldar and Tyrannid Armies
AnswerImperial Guard Eldar and Tau Chaos, Necrons, Orks, Tyranids and Dark Eldar are considered the "bad guys".
If you are talking about Orks off of Lord of the Rings, no they are not. They were created from dead remains of Elves and trained to kill and do evil.
Space marines Chaos space marines Necrons Orks Tau Space wolves Daemon hunters Chaos daemons Eldar Grey Knights Tyranids Blood Angles Dark Angles Dark Eldar
The four species in Dawn of War II are the Space Marines, Orks, Eldar, and Tyranids.
Eldar Space Marines Imperial Guard Dark Eldar Tau Chaos Space Marines Witch Hunters Gray knights Chaos Daemons Necrons Orks Tyranids
No they are the same size unless you take into account the extra modifications the 40k Orks have.
Eldar would win if they were at range (execpt howling banchess) but if the orks got in at close range they would win