I offer two criticisms of this essay:
First, this statement:
"But the ages of our congresspeople aren’t simply reflections of who voters determine is the most qualified. They reflect who the parties believe in, promote, and invest in."
This is a mild form of conspiracy theory. It attributes too much power to the parties and too little to the voters. True, the parties prefer incumbents to newcomers, but that is largely because incumbents always have an advantage over newcomers. Ultimately, though, elections are about getting the most votes, and the parties don't decide that -- the voters do. Take your plaint to the voters.
Similarly, this statement is problematic:
"But if Democrats want to spend the next few decades actually getting stuff done, they have to develop their party’s next generation of political talent — and that means empowering young candidates and letting them lead the party, and the country, into the future."
It's certainly true that every party needs to develop its young talent. But every organization has this responsibility, and in fact a solution to it has been around for millenia: start the young off on minor tasks and promote the talented as they age. Universities do this; corporations do this; why shouldn't democracies do the same? Many politicians (though certainly not all) start their careers in local offices, climb up through state offices, and then make the jump to the federal level.
My second criticism of this essay is its inappropriate reliance on identity politics. There is a problem here, but framing it as "Boomers versus Millennials" is divisive. I have never understood why Democrats prefer to shoot at each other rather than Republicans. There's no dividing line in Congress, with markers on the seats indicating where Boomers must sit and Millennials must sit. Why then must you insert an ideological dividing line where none exists in the real world?
Yes, older people are generally more conservative and stodgier than younger people; that's human nature. I do not argue that this makes them better or wiser, although I agree that, in general, older people are wiser than younger people.
I'm a Boomer; my generation made the same complaints when we were young. The political differences between my generation and its elders was greater than the current analagous difference. Eventually, some of us decided to do something about it. Those people entered politics and slowly worked their way up the ladder and eventually gained power. But it took several decades and a lot of work.
Your generation will end up running this country. The fate of much of humanity will fall onto your shoulders. Are you quite certain that you're ready for that responsibility? Indeed, should your concern be with power or with responsibility? How well does your generation understand climate change? The Gini Index? Balance of trade? Nuclear weapons treaties? If you were suddenly thrust into power today, would you not wish that you had had more time to learn before taking the burden of such heavy responsibilities?