(CNN) When South Bend Mayor Pete Buttigieg makes his pitch on why he, mayor of the fourth-largest city in Indiana, should get a serious look from voters who want to unseat President Donald Trump, he points directly at his lack of wrinkles.

He's a young guy, not an old guy, and to Buttigieg, that's the point.

"When you take a look at me, my face is my message, right? A lot of this is simply the idea that we need generational change, that we need more voices stepping up from a generation that has so much at stake in the decisions that are being made right now."

Buttigieg, who was born in 1982, would be the first millennial presidential candidate, if you go by the Pew definition. He's up against Bernie Sanders, who like potential candidate Joe Biden comes from the Silent Generation, born before the end of World War II. Along with the baby boomers and Gen Xers in between, it's a four-generation spread unseen in modern presidential politics.

Generations change slowly, and there are different definitions for when they start and stop. But this is the first full year of millennials to reach the constitutionally mandated age of 35 to take the office of president.

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