Welcome from Heidelberg Germany!
To convince your dad to let you wear a kilt, I would first show him pictures of people in kilts so he can see that they aren't a costume and can look good. Here are links to a bunch of pics
Dressy Kilt Pics http://www.xmarksthescot.com/forum/x...432/index.html
Casual Kilt Pics
http://www.xmarksthescot.com/forum/x...asual+pictures
Formal Kilt pics
http://www.xmarksthescot.com/forum/x...asual+pictures

If that doesn't work, remind him that you could be wanting to wear teen fashion that has little to no redeeming value such as huge baggy hang off your rear pants, gang colors, or extreme hair colors or styles. The kilt while different and not the norm has a long distinguished history and has been worn by numerous famous and important people over the years. Good luck in your efforts and let us know how things turn out.