I am very glad that you discovered your sexual orientation at the same time because of your liking for men in loincloths. Just like you, the same happened to me, only with me it was for the movie "The Jungle Book of 1994" and having my "first crush." I hope one day you will be encouraged to go out without a shirt and have confidence in yourself ;)
I cannot really say what started my interests in loincoths. It must be the time when my puberty started. I can remember that I saw some ducumentaries and read some books on foreign countries with picture showing men wearing various types of such gear. I was fascinated and still am, both with men and loincloths.
I soon started to make my own loincloths, first just two flaps, later I improved the design. I still wear my gear in summer when out for hiking or camping.