You can start as early as eight years old or as late as 16. Most girls' breasts develop between the ages of nine and 14. They can grow slowly or quickly regardless of when they start to develop. If you get your period and your breasts and nipples are totally undeveloped, you should see your doctor to just make sure that everything is on track. It's normal for breasts to feel sore or tender as they develop.
Many girls get stretch marks on their breasts.
This is because our skin can't always keep up with the growth happening beneath it. Stretch marks may start out pink or red and raised, but will eventually fade and be much less noticeable. Most girls' breasts and nipples are sensitive to stroking, touching, and kissing. Looking at, feeling, and kissing breasts, turns on a lot of people. Some partners are clumsy in the way they handle breasts and need to be told or shown how to do it in a pleasing way.