I'm scared about my !?

I am 12 years old. My bust size is 28 inches which equals 71 cm. I know I don't have big s and I don't want to either. Its just that I don't know if I should get a bra because there is another girl who is about the same as me and the same age and is wearing a bra but is taller. And a lot of other girls are wearing bras too. But then there are some other girls who don't have bras. I don't know what to do. Should I wait a little longer? And what is the speed of growth of ? Please don't answer rudely! I am just asking here!