David Walton has been cast in a new comedy pilot for CBS. According to The Hollywood Reporter, the Boston area native will costar in “9J, 9K, and 9L,’’ a show about a guy named Josh (played by “Royal Pains’’ star Mark Feuerstein) who lives in apartment number 9K in between his parents (who live in 9J) and his brother, sister-in-law, and their baby, who reside in 9L. THR reports that Walton (inset) will play the role of Andrew, “Josh’s successful, narcissistic and very competitive brother.’’ Walton, who starred in the NBC sitcom “About a Boy’’ and most recently appeared in the Showtime series “Masters of Sex,’’ grew up in Chestnut Hill and attended the Dexter School in Brookline and St. Paul’s School in Concord, N.H., before graduating from Brown University in 2001.