The usual threshold of 18 means that young people’s first chance to vote often coincides with finishing compulsory education and leaving home.
Away from their parents, they have no established voters to emulate and little connection to their new communities.
As they move around, they may remain off the electoral roll.
Sixteen-year-olds, by contrast, can easily be added to it and introduced to civic life at home and school.
They can pick up the voting habit by accompanying their parents to polling stations.
In Scotland, where 16- and 17-year-olds were eligible to vote in the independence referendum in 2014, an impressive three-quarters of those who registered turned out on the day, compared with 54% of 18- to 24-year-olds.
In 2007 Austria became the only rich country where 16-year-olds could vote in all elections.
Encouragingly, turnout rates for under-18s are markedly higher than for 19- to 25-year-olds.
Merely lowering the voting age is not enough, however.
Youth participation in Scotland might have been still higher if more schools had helped register pupils.
Governments also need to work harder at keeping electoral rolls current.
Some are experimenting with automatic updates whenever a citizen notifies a public body of a change of address.
Civics lessons can be improved.
Courses that promote open debate and give pupils a vote in aspects of their school lives are more likely to boost political commitment later in life than those that present dry facts about the mechanics of government.
A lower voting age would strengthen the voice of the young and signal that their opinions matter.
It is they, after all, who will bear the brunt of climate change and service the debt that paid for benefits, such as pensions and health care, of today’s elderly.
Voting at 16 would make it easier to initiate new citizens in civic life.
Above all, it would help guarantee the supply of young voters needed to preserve the vitality of democracy.
Catch them early, and they will grow into better citizens.