Typically the masterclasses are aimed at high school students. The ages vary between 15 years and 19 years.
No, all you need for the exercises, you will learn during the day.
Contact the participating institute closest to you.
Yes, 8 years ago, the UK masterclasses have started. Meanwhile they have been carried out in more European counties. Here is some feedback and evaluation. The EPOG WYP05 Masterclasses were the first European-wide masterclass event.