World's Youngest!!

In 1955 Boris Spassky became the youngest GM in the world at age 18. In 1958, Bobby Fischer became the youngest GM in the world at age 15 years, 6 months, 1 day. In 1991, Judit Polgar became a GM at 15 years, 4 months, and 28 days. In 1994, Peter Leko became a GM at the age of 14 years, 4 months, 22 days. In 1997, Etienne Bacrot and Ruslan Ponomariov became GMS at 14. Bacrot was the youngest FIDE master at age 10. Bacrot was 14 years, 2 months when he earned the GM title. Ponomariov was 14 years, 17 days when he earned the GM title. Teimour Radjabov became a GM at 14 years, 14 days. In 1999, Bu Xiangzhi became a GM at 13 years, 10 months and 13 days. In 2002, Sergey Karjakin (born Jan 12, 1990) became a GM at 12 years and 7 months. Also in 2002, Koneru Humpy became a GM at the age of 15 years, 1 month, and 27 days, making her the youngest female ever to become a Grandmaster.
In 1999 David Howell, age 8, defeated Grandmaster John Nunn at the Mind
Sports Chess Olympiad in London, becoming the youngest person to beat a
Grandmaster at chess.
In 2002 Fabiano Caruana, age 10, defeated GM Wojtkiewicz at the Marshall Chess Club in New York, becoming the youngest player to defeat a GM in the United States.

Hikaru Nakamura is the youngest American GM ever!

Hikaru Nakamura earned his third & final norm at the Bermuda International (GM-B) event, which concluded 5 Feb 03.  Nakamura scored 7.5-3.5 to finish in clear 2nd place in this 12-player Round Robin, just one-half point
behind the winner, GM Daniel Fridman (LAT-2572) with an 8-3 score.
At 15 years, 58 days, Hikaru is the youngest American Grandmaster ever, eclipsing Bobby Fischer's 1958 record of 15 years, 185 days.  Here is his 3rd round victory:
Nakamura, H (2520) - Moreno Carnero,J (2508)
Bermuda GM-B (Southampton BER), 02/06/2003
1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 O-O 6.Be2 e5 7.O-O
Nc6 8.d5 Ne7 9.b4 Nh5 10.Re1 a5 11.bxa5 f5 12.Nd2 Nf4 13.Bf1 fxe4 14.Nb3 Nd3 15.Bxd3 exd3 16.Ne4 c5 17.Qxd3 h6 18.Bd2 Nf5 19.Rab1 g5 20.Nc1 Ra6 21.f3 Nh4 22.Ne2 Rf7 23.N2g3 Bf8 24.Rb5 Be7 25.Reb1 Qf8 26.Rb6 Ra8 27.R1b3 Qd8 28.Qb1 Bf8 29.Be1 Ra7 30.Ra3 Ra8 31.Nf1 Nf5 32.Ne3 Nd4 33.Nxd6 Bxd6 34.Qg6+ Rg7 35.Qxd6 Qe8 36.Qxh6 e4 37.fxe4 Qxe4 38.Qh5 Bf5 39.h3 Rf8 40.Bg3 g4 41.Rh6 Bh7 42.Nxg4 Nf5 43.Rf3 Rxg4 44.Rxh7 1-0