your nose and ears continue to grow until you die...strange but true.
but that is not what you are upset about, nor do you really believe your nose is literally growing...
does your sister know of your behavior? It is not that uncommon for adolescent boys to be sexually curious about any female that comes into their lives. It does not mean you are a pervert.
If you continue to feel guilty about it though, you might want to seek counsel or forgiveness or both.
Jesus, scripture says, was tempted in every way like we are! Think about that one. He totally understands and totally forgives. You can go on free of all guilt and confusion. A conversation w a good pastor could help.
If necessary a conversation w a counselor might help too.