Yeah, apparently small boobs are not allowed on adults, lol.
All adult women must have balloon tits.
I remember there was a movement in Australia that appeared to outlaw A-cups in porn. Turned out it wasn't official, but the certification board did seem to use cup size as a measure of whether an actress "looked" adult enough to appear in porn.
This reminds me of the case of Nora Kuzma, who definitely wasn't A-cup, (she was 34D), was able, at 15, used a fake ID identifying her as 20. With that ID in hand, she was able do nude modeling, and the same year entered the porn industry. No one had a clue until the FBI raided her and her associates soon after her eighteenth birthday (they had apparently been monitoring her for more than a year. No one had a clue, in part because she was so busty. Today, only one film was made after she turned 18, Traci, We Love You, and it remains her only legal porn. It was also the only one she produced and so had the rights to distribute, all the others that had to be destroyed belonged to others. All this emphasis on petite a-cups and the most famous one who actually performed underage was anything but.