I argue with pro-contact pedophiles online, and many of them are into "youth liberation". While there's no necessary connection between them, it is a natural link. If minors should be allowed to make far more decisions for themselves, one decision they might make is to engage in sexual activity with adults.
I haven't studied youth liberation in depth. One grievance mentioned is that adolescents are sometimes forcibly returned to abusive homes. That is disturbing, and I would surely favor solutions to that problem if they are practical.
In general, youth oppression by parents and the state is not on the list of the world's top 100 problems. Infants start out totally incompetent, and over time they come into adult competence. They are gradually given responsibility by parents, even if the parents retain the final say legally. Wise parents tailor the responsibility they give to the particular child, based in part on how well they handle it. We can quibble about exactly where to draw the line legally, and when the child or the state should overrule parents, but there are no huge injustices waiting to be fixed.
In looking for common ground with my pro-contact opponents, however, I thought about youth being allowed to vote. I've decided (though open to counterarguments) that the voting age should be lowered to zero.
The main justification for a voting age is the concept of the informed voter. The truth is that very few voters are highly informed. Political questions are very difficult, and so naturally are choices as to which candidate should be elected. Many people would do better to find thoughtful and educated people who share their values and vote the way they suggest rather than trying to sort out all the complicated issues themselves. I suspect it's what many people do in practice.
While it's of course great if voters inform themselves and consider their votes carefully, legal restrictions make no sense. We've done away with literacy tests because of their discriminatory effect. The one limit we still have is the age limit. It is easy to enforce. And aggregated over a lifetime, it is not discriminatory, since no one gets to vote when they are young and everyone gets to vote when they come of age. But that doesn't mean it's a good idea.
So what happens when we give children the vote?
Initially children are likely to vote the way their parents tell them to. I see nothing wrong with that. Government policies should take into account the interests of children, and before they have developed their own opinions, who better to judge the interests of children than their parents? When they have developed their opinions, universal voting handles this transition beautifully. Older children can vote their own mind in the privacy of a voting booth.
Children who cannot read can vote the same way illiterate adults vote -- by recognizing patterns. Children who cannot reliably recognize patterns may not give meaningful votes, but if their votes are essentially random then they will cancel each other out. And the youngest children will not have mastered the ability to fill in the right number of bubbles clearly. They might scribble on the ballot, in which case it will be discarded. In practice, such young kids wouldn't ask to vote.
What are the drawbacks? Perhaps there are issues that would strongly influence children's votes that really aren't a good idea. A silly (I hope) example might be "free candy for kids". If it was a simple referendum the issue would lose based on adult votes, but in electoral politics things are more complicated. While adults would be primarily concerned with other issues, politicians might promise some version of free candy for kids to get the kid vote. For more reasonable questions like, "Should school have recess?", it seems fair for kids to be able to express their preferences by voting. I am confident that very few will turn into single-issue voters based on the right to have sex with adults.
Another exception we have to universal suffrage is people in prison, or convicted felons after their release. Denying them the right to vote is terribly misguided. Some people serving prison time are innocent. Others may be in prison for violating laws that society will come to feel are unjust, and they should be allowed to weigh in on the matter.
We have also created a perverse incentive for differential incarceration. Most felons in the US who have their right to vote restored register as Democratic:
(All the hard numbers are on the "pro" side).
This gives Republicans an incentive to tag more people as felons. In the extreme case, a legislature controlled by one party could find ways to turn large proportions of supporters of the opposing party into felons, thus giving them a permanent lock on power.
Suffrage should be universal.