(written from a Production point of view)
Spencer Eli Daniels (born 23 December 1992; age 26) is the young actor who played George Samuel Kirk in Star Trek.  However, this character is not in the final cut of the film. One scene featuring Daniels as Sam Kirk remained intact, but his character's name was changed to "Johnny." 
Daniels was born in Tarzana, California and has started his acting career at the age of ten. He appeared in the television series Mad TV (2003), Lyon's Den (2003), Judging Amy (2003), 10-8: Officers on Duty (2004, episode Flirtin' with Disaster, alongside Leon Russom and Joel West), The John Henson Project (2004), and Cold Case (2004, episode The Plan, with John Mahon, Robert Rusler, and Sam Witwer).
He played Billy Conroy in the two short films Billy's Dad is a Fudge-Packer (2004) and Billy Conroy Takes a Stand (2005), followed by an appearance in the It's Always Sunny in Philadelphia episode Charlie Wants an Abortion, where he played alongside Autumn Reeser. Also in 2006 he played the lead role in the short horror film Witchwise with Colby French and appeared in four episodes of The Office (which his father produced, while an aunt, uncle and Rainn Wilson were part of the cast), including the series finale (with Bill Hader and Ed Begley, Jr.).
Currently he filmed the thriller The Least of These (2008) with Star Trek performers Bob Gunton, John Billingsley, and stunt coordinated by Fernando Chien and the mystery drama The Curious Case of Benjamin Button (2008), where he played a younger version of Brad Pitt's character. Donna DuPlantier, Robert Towers, and stunt performers Max Daniels, Danny Downey, Jeremy Fry, and Marty Murray were also part of this film.