I'm not sure what sexism you mean specifically, but my skepticism has nothing to do with the specifics of the persona. Of course there are 16-year-old girl hackers. My wife once was one.

I doubt that the character is really a 16-year-old girl because she's telling Forbes she's a 16-year-old girl.

If 'k said he were a 16-year-old boy, I'd doubt he were a 16-year-old boy.

If 'k said she were a 33-year-old quant on Wall St., I'd doubt she were a 33-year-old quant. Etc.

I just seriously doubt that this character is giving any real identifiable information to Forbes.