The 26th Amendment to the US Constitution, adopted in 1971, guarantees that the right to vote shall not be abridged for reason of age as long as you are at least 18 years old. By why shouldn't 17-year-olds or 16-year-olds or even 12-year-olds be allowed to vote if they want to? Certainly I've met many teenagers who are more knowledgeable about and engaged with politics than the typical adult. And teens are obviously human beings and citizens with interests and rights just like everyone else. If for whatever reason James Madison had thought to stick a 15-year-old minimum voting age into the Bill of Rights, I think it's pretty clear that nobody would be sitting around in 2015 agitating to bump it up to 18. What would the reason be?

If pushed, I'm willing to go all the way and say that anyone regardless of age should be allowed to vote if they are capable of actually casting their own ballot. Denial of voting rights to children isn't top on the list of global injustices, since, thankfully, the vast majority of kids survive to voting age and ultimately get a chance for their voices to be heard. But it's still arbitrary and ridiculous.

We let under-18s participate in politics

Voting is, obviously, far from the only way a person can participate in the political process. Indeed, among adults, a person whose only form of political engagement is voting is relatively far down on the engagement/influence ladder. And right now there are no age limits on those other forms of engagement.

A 16-year-old is completely within her legal rights to:

Make a financial contribution to a political campaign

Volunteer to make phone calls or knock on doors for a candidate

Write letters to elected officials

Attend political rallies

Display bumper stickers, signs, and other campaign paraphernalia

There is not, in other words, a general prohibition on teenagers with strong political convictions attempting to influence the political process. In a republic, voting in elections is the baseline form of political influence for citizens. So if children are not barred from seeking to influence the system, why deny them this most basic form of influence?

Voting rules are not competency-based

A common objection to letting children vote is that they are not sufficiently wise or knowledgeable about political matters to vote. This may be true. But it's an objection to electoral democracy in general, not to letting teenagers vote. Electoral democracy is a fairly radical idea of reasonably recent vintage. One reason voting rights in the United States are so poorly protected is that the founding generation generally rejected the idea in favor of a republic where voting rights would be limited to property owners.

Over the years, many practical and intellectual efforts have been made to devise systems that would use voting as an accountability mechanism without going so far as to simply let everyone's voice count equally in the political process. But the post-1960s consensus in the United States is that voting should be a right of all adult citizens.

You don't need to pass a civics test to vote.

You don't need to have an IQ above a certain level to vote.

You don't need to show that you can accurately recite the candidates' slogans or platforms to vote.

Indeed, you don't even need to know what an election is about to vote in it. My guess is that a relatively small number of the people who cast a ballot for New York state comptroller or Texas railroad commissioner can accurately describe what the powers of those offices are.

Barring children from voting on competency grounds, in other words, implies rejection of the whole underlying premise of our current scheme of voting rights.

Extra influence for parents wouldn't be bad

Many people feel that it would be bad to let children vote because they would be excessively "bossed" by their parents and would de facto provide extra votes to large households. This seems empirically questionable to me, but also unobjectionable if it happens.

After all, a family of five contains more human beings than a family of two, so if the result of children voting were that the political system started giving more weight to the interests of five-person families than to the interests of two-person families, that would be a sensible outcome not some shady sleight of hand. Perhaps the child poverty rate would not be so high if children's interests were taken more seriously in politics.

The slope doesn't slip

If you're going to let 13-year-olds vote, then why shouldn't they be allowed to smoke? To drive cars? To have sex with adults?

This slippery slope logic is a mistake. Most age-based restrictions on activities are competency-based. You can see this because most of the things teenagers are not allowed to do are also things that drunk adults are not allowed to do. A drunk person is considered unable to operate a car safely and unable to genuinely consent to sex. But a drunk person most certainly is allowed to vote. You can vote drunk for the same reason you can vote in an election without knowing anything about the issues — our current conception of democracy prevents being barred from voting on competency grounds.

That means lowering the voting age has no implications for age restrictions in other areas where concern is driven by competency.

Democracy is a good idea

These days, the idea of democracy enjoys a high level of prestige such that even authoritarian regimes generally imitate its form. That wasn't always the case. There was a time when people — even ardent Republicans — regarded the idea of just tallying up the preferences of whoever happened to show up to vote as a self-evidently absurd manner of organize public affairs. Yet time has proven democracy to be an extraordinarily successful system of government. The countries that have achieved the highest living standards ever seen in human history — the United States, but also Norway, the Netherlands, Canada, Australia, Sweden, Denmark, etc. — all adhere to versions of democratic ideals.

But living up to those ideals has always required change and expansion of the definition of who deserves the franchise. It's time to do away with another taboo and start letting people vote regardless of age.