ANDY'S ANSWER: Well, I'm sure it doesn't seem very fair that your little sister seems to be developing faster than you are, but that's just the way it goes sometimes. Every person is different, and just because you are sisters doesn't mean that things necessarily happen at the same rate or in the same way. For instance, I have a friend who inherited her mother's shorter, rounder framework with a larger chest, but her older sister has developed with a more athletic build - taller, leaner and a bit smaller in the bustline like their father's side of the family. Both girls have grown into beautiful women and even though they are different, both of their bodies are normal and attractive.
You will develop at the speed that nature has in mind for you and the finished product will be great!