The Republican Party likely would crumble as a national force tomorrow if seniors in nursing and retirement homes stopped voting. Meanwhile, their their entire agenda serves to undo the biggest victories of the "War on Poverty" -- which primary benefited the elderly. You can argue that teens cognitive abilities on average do not match adults in their "peak" years, but you could make the same case against some older voters. The difference is, only one group has to live with the consequences of their current choices for generations.
Any argument against teens voting makes more sense when applied against older seniors voting.
Don't think a 16 year old has enough "life experience" to vote? Put her up against twenty 78-year-olds and let's see who figures out which stories in their Facebook feed are real first. You could easily argue that Americans who grew up without computers and smartphones are not equipped to participate as citizens in this society.
First of all, we already do that. Young defendants are already sentenced to life in prison by a government they had no hand in choosing. Second, as a society we see the wisdom in meting out the privileges and responsibilities of adulthood in pieces. 18 year olds in Florida can buy AR-15s but not beer. 23 year olds can drive tanks but not rental cars. Believing that young people deserve a say in our democracy is not to say that 16 year olds are full-fledged adults. They're not! That some of these distinctions are arbitrary and hard to draw doesn't absolve us of the moral harm of denying capable teenagers a voice.
I see from my previouslies that 14 years ago there was a proposed California amendment to give 14 year olds "half a vote". I never heard anything about it again because it died in committee and never came to a vote or debate.
Those kids would be 28 by now.