First welcome
Being a teenager is a challenging thing to do.Not only you have to find your personality and try to find your place in the world,but you have immense amount of peer pressure and conflicting information from media.none of it is helping in stabilization of sexual maturity.
Some people "awaken" sexually later then others.do not worry about not being aroused yet,arousal depends not only on appearance ,but something more.there should be some connection to be aroused.Dont jump into relationship looking for arousal , you are way too young to call yourself asexual .you will meet a right person and things will be all right
Stay well