It's not because the 44-year-old Republican is obviously closer to that generation than Sanders, who will turn 75 before Election Day.
No, it's because Rubio embodies the ethos of millennials, which the Washington Post snidely dubbed the "Participation Trophy Generation." Hey, it's an unflattering stereotype, but trend-story hazing is a rite of passage for each generation coming of age.
As a Generation Xer, I recall being told how lazy and entitled we all were, as well. And some of us were, just like snot-nosed 20-somethings who act like they're ready to run the company on their first day just because they know what Snapchat is. (Hey, I'm 90 percent sure that I do, although I've clearly never used it).
But Rubio is the ultimate "Participation Trophy" candidate of 2016. He's gone an embarrassing 0 for 4 in the first nominating contests. And yet he still parades around like he's the frontrunner, enabled by the desperate GOP establishment that's determined Rubio is their last, best (and dreamiest) hope against Donald Trump.
When Rubio finished third in Iowa, he had the chutzpah to give a victory speech. It wasn't a bad strategic move, and plenty of pundits ate it up. Politics is often about faking it till you make it, and the freshman senator has that motto down cold.
But then Rubio went on to take fifth in New Hampshire. He failed to capture a single delegate in South Carolina and still gave another "victory" speech. Donald Trump then crushed him 2-1 in Nevada.
And yet Rubio backers are out there goading other candidates to drop out, like Ted Cruz, who actually won something (Iowa) and John Kasich, who pulled out a surprise second-place finish in New Hampshire and could do well in the Midwest primaries ahead. New polling shows Rubio is even losing to Trump in his home state of Florida.
Rubio has the swagger of a candidate who's never lost anything, because he hasn't until now. When Republican powerbrokers have been pumping you up as the fresh face of the party -- the only one who can defeat the Democrats -- it goes to your head.
People are always quick to blame parents for raising selfish millennials who crack under pressure. Maybe the Republican establishment deserves some for emboldening a green freshman senator. Because Marco Rubio obviously doesn't seem ready to be commander-in chief.