Why are my brothers allowed to do more then me?

So I've got three brothers two older and one younger. The younger one lets call him Robert is only younger by nine months and we're often mistaken as twins, he is even taller then me. My two older brothers Matt and Paul are 23 and 17. I'm sixteen at my age they where allowed to go to party's and go out with there friends even Robert is allowed to that. But my Dad refuses to let me go anywhere near guys or Party's. I actually think he prefers my brothers because they play sports which I'm totally incapable of, I'm clumsy, too clumsy for any sports. I'm a klutz. I love my Dad and after my Mum died when I was 9 I tried to take care of everything around the house but specially Robert. So I thought I proved that I'm responsible. What do you think?