JayXx / Aug 13 2009 20.00
Its different for every person, but, as with every change in your body, it all happens in sync with every other change. You should judge from when your period started (if it already has started), and in a few years, they will be fully developed. However, like I said, some girls are different, and this is just general advice. Usually, they've developed by the time you're17-20.