By Scott Conroy - October 10, 2012

For the third time in as many presidential election cycles, the vice-presidential debate on Thursday night will showcase two candidates who came of age -- both personally and politically -- in different eras.

The generational gap between 69-year-old Joe Biden and 42-year-old Paul Ryan may not be at the forefront of either campaign’s debate practice sessions, but it is could have an impact on “perception battle” from the moment that the two men take the stage.

In the 2004 VP debate, the age difference between John Edwards and Dick Cheney was a relatively modest 12 years, but the physical distinctions between the youthful, energetic Democrat and the dour, white-haired Republican could hardly have been more striking.

Going into that contest in Cleveland, Edwards -- a charismatic former trial lawyer -- was widely expected to outshine the incumbent with a history of heart problems and a reputation for being proudly cantankerous.

Instead, Cheney more than held his own in a seated format that suited him well. He was able to draw attention to Edwards’ status as a relative newcomer on the national political scene via a rehearsed line intended to highlight his opponent’s poor Senate attendance record.

“The first time I ever met you was when you walked on the stage tonight,” Cheney said to Edwards in one of the debate’s most memorable moments.

The assertion was later shown to be technically untrue, but during a debate in which the war in Iraq and other national security-related policies were central topics, it helped reinforce perceptions of Cheney as an experienced Washington hand, while Edwards was untested.

In what was indisputably a “change” election four years later, Sarah Palin sought to turn her relative youth into an advantage. At an Ohio rally three days before she squared off against Biden, the 44-year-old Palin drew attention to her Democratic opponent’s senior status.

“I've never met him before,” she said of Biden. “But I've been hearing about his Senate speeches since I was in like second grade.”

Going into their face-off in St. Louis, Palin benefited from coming into the debate with the lowest expectations of any vice-presidential candidate in memory.

Her performance, in which she winked for the cameras and avoided answering many of moderator Gwen Ifill’s questions directly, was largely deemed a success in light of her ability to stand toe to toe against a Washington fixture who had spent decades steeped in the intricacies of domestic and international policy.

Biden is now four years older, of course, and in Danville, Ky., on Thursday night he will be matched against an opponent two years younger than Palin was in 2008.

To put that age disparity into starker perspective, when Biden was first sworn into the U.S. Senate in 1973, Ryan was not yet 3 years old.

According to Obama campaign officials, the generational gap between the two candidates has not specifically been factored into the preparation Biden has been undertaking since Sunday in Wilmington, Del.

Maryland Rep. Chris Van Hollen has been playing the role of Ryan in hours-long mock debate sessions, which have been fueled by caffeinated drinks, Gatorade, and animal crackers. At 53, Van Hollen is more than a decade Ryan’s senior but has been in Washington four years less than the GOP vice-presidential nominee.