One of the first signs of puberty is breast development. Many girls start to get "breast buds" (mounds or bumps around or under the nipple) at 11, but that’s average. If you’re a few years younger or older than 11 when you develop breast buds, that’s totally normal too.
Next stage in breast development, your entire breast will start to get larger. Your nipple and areola (the area around the nipple) will get darker and form a separate, small mound. This whole process, from "flat" to "finish," takes from 2 to 3 years. Some girls develop more quickly than others, and it’s not unusual for one breast to grow faster than the other. Sometimes it can take a while for things to "even out." But even adult women have one breast that’s bigger than the other.
Breasts get a lot of attention during puberty because they’re new, and not everyone gets them at the same time. Remember that everyone’s breasts are different. What’s important is the way you feel about your breasts and that, whatever their shape or size, you come to accept them as another unique and beautiful part of you!