Nikolas Cruz, charged with fatally shooting 17 people in Florida's...

Nikolas Cruz, charged with fatally shooting 17 people in Florida's Marjory Stoneman Douglas High School, appears in court last week. Credit: AP / Mike Stocker

So just how old is old enough to know better, and just how young is too young to care?

Those are the questions up for debate as some lawmakers in Washington and Florida look to increase the age at which Americans can buy semi-automatic rifles to 21. It’s a question on which the nation has gone back and forth over the years for all kinds of liberties, from voting to drinking to smoking to guns.

Is an 18-year-old a full citizen of the United States? Does the equal protection clause in the Constitution allow us to bar one group of full citizens from a liberty others enjoy? Is it reasonable to say an 18-year-old is mature enough to vote and to decide to serve in the military but not mature enough to buy a beer, or a smoke or a semi-automatic hunting rifle?

Nikolas Cruz, 19, has admitted killing 17 people in a shooting massacre at Marjory Stoneman Douglas High School in Parkland, Florida, earlier this month, police said. In the rush for answers, and ways to prevent more mass shootings, one of the ideas gaining traction is raising the age for buying semi-automatic rifles from 18 to 21. That would match the federal law on buying handguns from licensed dealers.

Raising the age makes some sense, because many young men are intellectually and emotionally immature testosterone bundles with wild impulses and iffy cause-and-effect reasoning. We know this because the science says so, and because our experience does, too.

Even so, it feels wrong to bar people who can vote and serve in the military from exercising other rights practically all Americans enjoy. Which makes me wonder whether I haven’t been looking at the whole thing upside down for years.

I’ve always argued that age limits higher than 18 on purchasing alcohol and cigarettes were inappropriate, but maybe it’s the laws that let people under 21 serve in the military and vote that make no sense. Maybe 18 is too young to be considered a fully enfranchised citizen in general, even though it may be for some.

We’ve gotten used to the voting age being 18, but letting people younger than 21 vote is fairly recent. The 26th Amendment, making the voting age 18, was not ratified until 1971.

The movement for the change grew out of the anti-war protests of the 1960s. Americans argued that people were being drafted to die by politicians they couldn’t choose or discard, and that this was wrong. Fair enough.

But most wars turn out to be foolhardy and useless, something many of us realize as we age. It’s true that fearless young men are easiest to enlist in these wars, but by that logic we’d send 12-year-olds.

What’s more, as we’ve moved from the era of pitched infantry battles with rifles and cannon to technological wars, military policing operations and counterinsurgencies, maturity, judgment and expertise are increasingly necessary in our armed forces. Youthful abandon is no longer the military asset it was in the 1800s.

Should the age at which we can serve in the military, vote, buy guns, drink liquor and smoke cigarettes all be exactly the same? Maybe. I’m not sure. It seems wrong to deny certain liberties to citizens who’ve fought for our country with deadly weapons because we fear they’re too young to make good decisions. But it also seems crazy to give too much leeway to immature people.

But the fix no one seems to consider is raising the age at which one can serve in the military, buy a weapon or vote to 21, and setting the smoking and drinking age there, too.

The military age limit might save more lives than age limits on smoking, drinking and buying civilian weapons combined.

Lane Filler is a member of Newsday’s editorial board.

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