Radjabov is not American, is he? Notice the original post said youngest US grandmaster ever. I think Radjabov is from Azerbaijan.
I didn't see the article, but I think it refers to Hikaru Nakamura, who became a GM last month.
See this link:
http://www.nscfchess.org/hikaru_gmnorm3.htm
He was about four months younger than Fischer was when he became a GM.