this is silly to even think about, im not trying to insult you, but not only do i think its incorrect to have any kind of sexual experiences with anyone related to me, be it sister or cousin, i just dont think its right. and on top of that, shes 9? you just need to tell her no, just because she asks doesnt mean you need to show her your penis... like others have said, i doubt any other family members would be happy with what is happening.
and i dont understand why youre telling us youre horny all the time, do you think that being horny justifies having such an experience? and does the fact that youre telling us youre horny tell us that you are hoping for something sexual to happen?
sorry im dont mean to rant, but i just think its a VERY bad idea to do what you are considering doing
Little kids sometimes play "doctor" or find other ways to agree to show each other their private parts, there's a kind of innocent curiosity about that, but when you are 13 you are old enough to know what you are doing and you must know, really, that it's wrong for you to be showing yourself to a 9 year old. If any of the adults in your family were to find out about it you'd be wasting your time saying "but she asked me to" because they would most likely take the view that she was too young to understand but that you should have known better.
i would suggest not doing it, i personally think she is just to young. I understand that you're horny all the time most people are at your age but just cuz you're horny doesnt mean you should show her.