I feel something is wrong with me.

We are three sisters. I am 25 F and my sister 24F and one 16F. Whenever someone meets us, their first question is who is the eldest then they almost always say she looks the youngest and my middle one looks elder. It might be a small comment but it makes me feel conscious i feel i don't want to do anything that they can make fun of me. I am adult but I am fed up hearing i don't look like one and then they laugh which looks like they are making fun of me. My height is 4' 11, i know it's short and weight around 45. But my sisters have broader body, more muscles. These days i feel anxious, thinking is she trying to show she is the one who can take responsibilities. I don't like it when I don't feel valued the only way I feel valued when people come and ask me. If that doesn't happen it makes me feel am i dumb? Am I not exciting person to ask anything? Why they went to her? I Maybe because I think I am smarter, more responsible, intelligent not her. Honestly I think it's not about her, it's me who doesn't know how to handle myself. It's not jealousy it's my hollow self that extracts value from others but breaks when it doesn't happen.