It will always vary from person to person and factors such as when you started puberty, what your diet is, genetic factors, and countless others. I would say just be happy with who you are and what you have and dont let anyone tell you otherwise.
32A or 34A would be average bra size for a 12 year old girl.
34B
There is no average since each girl/woman is different and breast size is based on DNA.
32B
32A
There really isn't an "average" size bra for a ceratin age group. Most girls, however, are about a A- to a B-Cup by the time they are 13 years old. Still, it is normal for a girl to be smaller or bigger than that.
D
34A
average would be 32B
30- 36
1AA
Every girl is different! And at 16, many girls (women) are fully developed. So if a B-36 bra fits you, then it is a good size for you. Many mature women wear an A cup, and many wear a DD - that's the beauty of diversity!