Prepped at Scarsdale High School in Scarsdale, New York. Other notable Scarsdale High School alums include Amazon President and CEO Andy Jassy (Class of 1986), Academy Award-winning screenwriter Aaron Sorkin (Class of 1979), as well as co-founder and longtime CEO of Men’s Wearhouse George Zimmer (Class of 1966).

Three-time New York State High School Hockey Coaches Association All-State selection as a forward, earning first-team nods in 2014 and 2015, and a second-team honor in 2013.

Grew up playing junior hockey with (and against) Charlie McAvoy, who eventually became the 14th overall pick in the 2016 NHL Draft and helped the United States win a gold medal at the 2026 Winter Olympics. Charlie even caddied for James in a Korn Ferry Tour event in 2020.

Did not start taking golf seriously until his sophomore season at Yale University, as he also played safety for the football team his freshman season (fall 2015).

Was on a pre-med track academically at Yale. Opted not to take the Medical College Admission Test in summer 2019 because "it expires in two years... I'm going to be playing golf longer than that."

Grandfather, Dr. James A. Nicholas, was an orthopedic surgeon and physician for the New York Jets, New York Knicks, and New York Rangers who, according The New York Times, was "a pioneer in the treatment of athletic injuries who was best known for performing four knee operations that saved the celebrated career of Jets quarterback Joe Namath." He also founded the world's first hospital-based research and clinical center for the treatment and prevention of sports injuries, the Nicholas Institute of Sports Medicine and Athletic Trauma, in 1973, and it was named for him in 1986.

James' father, Dr. Stephen Nicholas, is also an orthopedic surgeon and succeeded his father (James' grandfather) as the director of the Nicholas Institute of Sports Medicine and Athletic Trauma in 2001.

Youngest brother, Brian, was drafted by the Sioux City Musketeers the No. 8 overall pick in the 2021 United States Hockey League Draft as a high school junior. Brian also committed to the University of Michigan.

Younger sisters, Erin and Michaela, played collegiate field hockey. Erin was a decorated player at Middlebury (Vermont) College, where she made history as the first player to earn New England Small College Athletic Conference Player of the Year honors three consecutive years, was named the 2018 and 2019 National Field Hockey Coaches Association Player of the Year, and led Middlebury to four NCAA Division III national titles (2017, 2018, 2019, 2021). Michaela was a walk-on at Franklin & Marshall College, an NCAA Division III athletics program in Lancaster, Pennsylvania.

Younger brother, Stephen, played collegiate golf at Franklin & Marshall College for three seasons (2017-20), winning once as an individual.

Played collegiately for four seasons at Yale University (2015-19), winning five NCAA events, highlighted by medalist honors at the 2019 Ivy League Championship. Named the 2018 and 2019 Ivy League Player of the Year, a 2018 and 2019 All-Ivy First Team selection, and a 2018 All-America Scholar. Also won three consecutive Bosordi Student Championships.

Named the 2017 Metropolitan Golf Association Player of the Year, following in the footsteps of past winners such as decorated amateur Steward Hagestad (2016), and PGA TOUR member and 2020-21 Korn Ferry Tour graduate Cameron Young (2015).

Qualified for match play at the 2017 U.S. Amateur Championship, but lost in the first round.

Won the individual state title as a senior at the 2015 New York State Public High School Athletic Association, taking the title by one stroke and appearing on SportsCenter for an incredible chip shot from a greenside pond.