Stephen Yellin posts a minutiae-filled analysis of Senate, House and gubernatorial races across the country almost weekly on Daily Kos, the most-trafficked liberal political blog on the Net. Other posters laud his thoroughness and debate his conclusions. He has landed a spot as a political operative with a major Democratic presidential nominee. He's walked precincts, volunteered for campaigns and run for office. He is also 15 years old -- too young to drive to his local polling station, let alone cast a vote there. Yellin is just a sophomore in high school, but in the blogosphere he is already a...