Answer by taking a quote from the following article:

Nomo was born into the working-class Osaka family of Shizuo, a fisherman and postal worker, and Kayoko, a part-time supermarket employee. As a youth, Nomo was shy and withdrawn, although passionate about baseball. He developed his corkscrew-style pitching motion in order to impress his father while playing catch. He believed that rotating from having his back turned to his target would help him add speed to his pitches.

The tornado delivery that baffled batters in Japan had the same effect on major league hitters, and he led the league in strikeouts in 1995 (while finishing second in walks) and was second with a 2.54 ERA. He struck out 11.101 batters per 9 innings to break Sandy Koufax's single-season franchise record of 10.546 in 1962. He also started that year's All-Star Game, striking out three of the six batters he faced. But he only barely won NL Rookie of the Year honors that year over future MVP Chipper Jones, as many voters felt that his Japanese success made him anything but a rookie, although he qualified by Major League rules. Nomo had another fine season in 1996 which was capped by a no-hitter thrown on September 17 in the unlikeliest of places, Denver's Coors Field, a park notoriously known as being a hitters' park because of its high elevation, semi-arid climate, and lack of foul territory. He was the last Dodger to throw a no-hitter until Josh Beckett completed one on May 25, 2014. Nomo also found commercial success in America. Nomo had a signature sneaker, called the Air Max Nomo, produced by Nike in 1996. Also, he appeared on a Segata Sanshiro commercial for the Sega Saturn in 1997. As batters caught on to his delivery, his effectiveness waned a bit in 1997, although he still went 14-12, joining Dwight Gooden as the only other pitcher to strike out at least 200 batters in each of his first three seasons.

When did he begin playing baseball?
1995