srosendaal Thank you very much for your inquiry. We are very grateful for your interest in our program.
As you have noted, we are only able to offer internships to university students and recent graduates at this time. The hiring companies we work with tend to use internships as an evaluation tool for potential full-time offers. As high school students would be ineligible for these full-time offers, the hiring companies limit the eligibility criteria for their internships accordingly. I suspect that many internships outside of our program have these restrictions for similar reasons, but I cannot say with 100% certainty that programs for high school students do not exist.
Depending on your age and nationality you may be eligible for a Working Holiday Programme, or you may also be interested in studying abroad at one of many Japanese language schools throughout the country. In any case, I am very sorry that we do not have any resources to share regarding internships for during your gap year.
I hope this helps answer your question. Do you have any other questions or concerns? If there is nothing else we can do to assist you at this time I will go ahead and lock this thread after 48 hours.