Different sources give different dates as the birthday of John Cabell Breckinridge, sometimes January 21, sometimes January 16, but at least the year is clear: 1821. When he became the 14th Vice President of the United States on March 4, 1857, he was barely 36. He remains the youngest vice president ever to serve.
Son and grandson of successful Kentucky politicians, young Breckinridge was an attorney, Mexican War veteran, and noted member of the US House when tapped for the second spot under James Buchanan in 1856. "For Breckinridge, however, the move into the vice presidency proved to be a massive step downward," wrote John Marhsall Prewitt in The Vice Presidents: A Biographical Dictionary. (1998). "... the president pointedly ignored him. Worse yet, within a month of the inauguration, Buchanan not only denied a request from Breckinridge for a private audience but insultingly told the vice president to call instead on the president's niece. Breckinridge was outraged at this treatment -- resulting, apparently, from Buchanan's smoldering resentment that Breckinridge had originally supported Pierce and Douglas at the nominating convention -- but could do nothing."
The office didn't get any better for Breckinridge, dragging on for the next four years as the country verged on falling apart. In 1860, he ran in the infamous four-way race for the presidency as the nominee of the southern wing of the Democratic Party, losing to Lincoln. In March of 1861, the Kentucky legislature sent him to the US Senate, where he was an outspoken opponent of Lincoln's policies:
"Mr. President, gentlemen talk about the Union as if it was an end instead of a means," he said on the Senate floor on August 1, 1861. "They talk about it as if it was the Union of these States which alone had brought into life the principles of public and of personal liberty. Sir, they existed before, and they may survive it..." See here for the full text.
The next month, while Breckinridge was visiting Kentucky, the heads of the now-unionist state legislature called for his arrest, and he "went south" (after which the Senate expelled him). For the next four years, he served the CSA with distinction, mostly as a field commander but eventually as the last Confederate secretary of war. At the end, he opposed continuing the struggle as a guerilla war. "This has been a magnificent epic; in God's name, let it not terminate in a farce," he said.