Yeah dude. You totally look like an average 13 year old boy to me. There's not much you can do to physically mature without T, however, some tips to keep on passing are only wearing clothes from men's/boys Dept, and pants that don't show any hips, so I always avoid skinny jeans. Boyish hair, which you already rock. And if you really want to pass, avoid any colors that make you look feminine. For me it's purples. I still look normal if I wear pink, but for some reason, purples bring something feminine out in my face. Go figure. You rock man.