I'm not sure that works unless all kids have their birthdays at the start of the tax year.
The tax thing isn't something I hugely care about - I was just pointing out that there would be some young people paying tax. I think 16/17 year olds are starting to contribute to adult society - many of them are working, even if they're not earning huge amounts of money. They're having to make decisions about whether they go down a practical work route, or study. Whether they go to University and rack up huge loan debts that the majority of older voters don't have. Plenty are a lot more switched on that many of the adults I know, and given so many of the issues society faces are going to have a huge impact on the next generation, I'm quite happy that they have some input :)