You’ve not thought this through. Think about it, how many 16 year olds join the workplace on their 16th birthday?
So even if they “could” earn £14k a year (or more) the chances of them receiving that on a pro rata basis between leaving school and their 17th birthday is pretty low.
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 :)