I don't mind the questions, but I'll say that I am not entirely sure I understand them. Children can leave school at any age, or not attend at all, but it is their parents' decision. My father says that I have to stay until I have obtained my Certificate of Wizardry, for which I must pass my examinations at the end of the fifth form. I shall be sixteen then, I hope, but others might be older, if they started school later, or were ever kept back, as many of the mudbloods are at first.
I'll admit that most boys from families like mine go into the sixth to sit the Advanced Certificates, but I don't care to. Some others don't take examinations at all, they leave at fourteen or so to take up apprenticeships of various sorts. I'm not certain what a NEWT is, as you can't mean the creature.
I hope you'll forgive my incredulity, but a law against 'underage magic' seems rather like a law prohibiting children from using their legs! I did my first magic at four, and after that had lessons with a tutor to help me control it, and I must use it hundreds of times every day - from conjuring washing-water in the morning to lighting a candle to see my way to bed at night. And what of the children who don't go to school at all, but continue to be taught at home? It makes sense as a law prohibiting the mudbloods from frightening their muggle relatives, but little else. Are you certain it applies to our sort? Perhaps your parents are...unkind? Uncommonly strict? Or is it the opposite, if you're waited on hand and foot instead? unusual.