AJ is most likely a boy because the options provided are all gender identifiers, and "BOY" is the only option that directly refers to a male. The other options, "MEN," "GIRL," and "WOMAN," refer to multiple males, a female, and multiple females respectively, but none of them specifically identify a single male individual. Therefore, based on the given options, the most appropriate answer to the question "who is AJ?" would be "BOY."