Well if your talking bra sizes then... A A34 bra size is what most girls 12 to 13 wear. A B36 bra size is the bra size right after the A cup.
If the bra is not the right size or fitted right, then it can be extrememly uncomfortable. I personally, have a few bras that I hate wearing, mostly because they aren't the perfect fit. It is advised to go and get a bra size fitting (at Victoria's Secret, they do it for free). Once you find the right size and right bra for your body, you won't even notice you're wearing one!
The biggest bra size that us girls can have so far is 38kkk
you can get a bra measure from primark
Your only option is to guess the girl's bra size. If you are not buying her a bra, you don't need to know her bra size. Try to find out something that's important to her instead.
36A, but every one is different
Your bra is just the right size
In order to make sure that a 34B bra is your size, you should get a professional to fit you for a bra, retailers like Marks and Spencer offer bra fittings and can measure you to make sure that it is the right size for you.
No, but there are preteen bras that would be in the size of an AAA bra size. It would probably be in the size 12-14 bra.
You can't. All you can do is guess.
Bra size is more a function of breast size and chest circumference than age.
You can go to the mall or a shop and go yo the bra side with who ever you went with and try to find out what size you are or go to a bra place and have someone mesure you to get the right fitting bra