Sure, sure. We know it might seem like a cop-out to say that a political system is the antagonist rather than any particular character – but let's stop and think about it for a minute. Who else might be the antagonist here? We could say Bheki or his friend John are antagonists, since they seem to hate Mrs. Curren so much and are quick to fight others (remember how John beats the smack out of Vercueil?). Still, they turn out to be pretty sympathetic characters in the end. They're just kids, after all; we could say that they turned out the way they did because of the system of hatred they grew up in.
When we think of other characters that are the "bad guys," we automatically think of all of the officers in the novel who perpetuate the Apartheid system. There are the two officers who force Bheki and John into their bike accident and there's the officer in Gugulethu who doesn't seem to care about the horrors going on around him. But maybe the most striking example is the gang of officers who come to Mrs. Curren's house in search of John. Do these people seem to have any redeeming qualities? No. They do what they're paid to do – to "keep order" (keeping order, though, seems to include destroying the lives of lot of innocent people). Are these people bad people, deep down? We'd like to say yes, but we don't really have that much information on them as individuals. What we can say about them is that everything that's bad about them stems from the jobs that they're required to perform, and it's the system of Apartheid that gives them these responsibilities. As a result, we're still going to go ahead and say that Apartheid is the true antagonist in Age of Iron.