Martin Luther King, Jr. was still a young man when he made his famous "I have a dream" speech, and he was younger still as he built up to the stature in the Civil Rights movement that could put a million people in the Washington Mall to hear him speak. He didn't live to be 40 years old.
He accomplished something that simple minded political science says should be impossible. He convinced a group with a political majority to end the legalized oppression of blacks in a country where the formal barriers to black political power seemed insurmountable. It would have been impossible if he had simply played by the rules.
He isn't the first to accomplish this end. Suffragists had done it. The people of India had done it. The lower classes of English had accomplished it. His own efforts were rooted in the knowledge of history that this was possible and he studied the methods used to achieve it. Those aged 18-20 achieve it.
Martin Luther King, Jr. won, ultimately, because he triumphed in the world of ideas, and because he got people to pay attention. The economist's notion that people always act in their own self-interest, while very useful in the economic sphere, is a less than accurate description of how people act in the world of politics. People routinely favor policies, good and bad, which are not in their narrow self-interests, out of a belief that it is the just stance to take.
These days, we still have young stand outs in the world of politics. But, today, most of these people, Andrew Romanoff in Colorado, for example, are remarkable as much for their mastery of the rules of the game and the players in it, as for changing ideas. Our political system has largely co-opted or defeated the rebels who seek to accomplish the impossible through direct action. Political outsiders capable of rallying crowds, bringing about change, and changing the psyche of a nation are rare. I'm hard put to identify any today, although perhaps there are some, and there are many who aspire to King's model.