Will youth be a winning ticket for Democrats in 2020?

I arrived at Beto O’Rourke’s Austin rally last weekend two hours before it was due to begin, or about 3½ hours before O’Rourke got there, but Jenna Chang, 18, and Catherine Moring, 17, were already dancing together in front of the empty stage.

Chang and Moring, seniors at Marcus High School in Flower Mound, drove down, parked in the lot at the LBJ Library and rode scooters to the rally.

Flower Mound is a Republican suburb, home to state Sen. Jane Nelson and state Rep. Tan Parker. Moring’s parents are Republicans. Flower Mound straddles Denton and Tarrant counties. Denton County went for Donald Trump over Hillary Clinton by a 20-point margin. U.S. Sen. Ted Cruz, R-Texas, beat O’Rourke there by 8 points. Trump won Tarrant County by almost 9 points. O’Rourke beat Cruz there by seven-tenths of a point.

O’Rourke, the 46-year-old former congressman from El Paso, likes to brag on the presidential campaign trail that one of the reasons he did as well as he did against Cruz — losing by 2.6 points — was that “the state saw young voter turnout up 500% over the last midterm election.”

An AP Fact Check found that to be an exaggeration, determining that voter turnout among those under 30 in Texas was up 234% over 2014.

For a while now, politics in Texas has been dictated by a white gerontocracy — the older voters, whiter than the rest of the polity, who are most likely to vote.

But there is a catch.

"Older people vote with a vengeance, but they eventually do die," Rice University political scientist Bob Stein told me. "What's the rate at which people 65 and older are leaving the electorate? It’s 4.5 percent every two years and has been pretty steady — it’s slowed down a little bit because of Medicare, Medicaid, ACA — and those are disproportionately Republicans."

Donald Trump was 70 when he was elected president, a year older than Ronald Reagan when he was first elected. Reagan inspired a generation of young Republicans.

But Trump appears to be having a quite the opposite effect with younger voters.

On Tuesday, Julián Castro, another Democratic presidential candidate from Texas, who is 44, was asked by Rachel Maddow, "If you won and became president you’d be the youngest president since JFK, the second-youngest ever elected. Is youth part of what you have to offer as a candidate?"

"Yeah, I think so," Castro said, before politely pointing out that "in the modern era of presidential politics, since 1960, JFK was 43, Bill Clinton was 46, Barack Obama was 46 or 47. I would be 46. I don’t see that as particularly groundbreaking, because that’s actually been the norm."

Groundbreaking would be Pete Buttigieg, 37, the mayor of South Bend, Ind.

Groundbreaking would be Joe Biden, who is 76, or Bernie Sanders, who is 77. Despite their age, Sanders' Democratic primary campaign in 2016 was something of a young people's crusade, and Biden was hailed as a hero by graduate students at the LBJ School when he spoke there in October 2017.

Last month, the U.S. House defeated an amendment to lower the voting age to 16, but a majority of Democrats — including, in Texas, Castro's brother, Joaquin, and Austin's Lloyd Doggett — voted "yes," along with exactly one Republican, Michael Burgess, whose district includes Flower Mound.

That's not going to happen, but it is a sign that Democrats see their future in younger voters. They are probably right, but history can be hinky.

I'm old enough to remember the 1968 movie “Wild in the Streets,” in which the voting age is lowered to 14, a 22-year-old rock star is elected president and everyone over 35 is sent to re-education camps with LSD in the water coolers.

Four years later, I was among the first generation of 18-year-olds to vote in a presidential election. It was 1972, the Nixon landslide.