Setting imaginary tests before allowing enfranchisement is an essentially 19th-century idea. The basis of the principle of universal suffrage that replaced it is that we no longer believe voting is a right that belongs to individuals on the grounds of their competence to exercise it. Instead, it is a right that belongs to each of us because we are members of a democratic political community, and will have to live with the consequences of the decisions that are made by politicians on our behalf. If we suffer the consequences of those decisions, we should have a right to express a view about who gets to decide. That applies to children just as much as adults.

Perhaps, instead, the argument against letting children vote is less a principled one than a pragmatic one. Surely more adults are likely to understand what is at stake in an election than a group of schoolchildren. But that depends a great deal on how we conceive of the groups in question. It is striking how often sceptical audiences jump to the conclusion that lowering the voting age to six would mean giving six-year-olds a decisive say in the running of the country. That is absurd: the lower age group would be a small minority of children overall, just as children would still be a minority of the overall electorate. Older voters in any instance can always outvote the young. But if we take children in education as a whole, there is a good chance that some groups will be better informed than many adults. They have the time and the resources to learn what is at stake if they want to. No one can be obliged to take an interest in politics, but that is as true of adults as of children. The difference is that children in school are better placed to make up the gaps in their knowledge.

The question of competence – and the difficulty of using it as an argument against extending the vote to children – is especially acute in ageing societies such as our own. As the population ages, so the number of voters suffering from dementia and other forms of cognitive decline rises. But we don’t take the vote away from old people, and we don’t apply tests of competence to individuals in their 80s and 90s. Again, it is very striking how often I find that when pressed on this point, audiences will say that rather than giving votes to children it would be better – safer? – to disenfranchise elderly people. The 19th-century assumption that we ought to discriminate on grounds of competence has not gone away.