Short answers, pulled from the story.
Shōnen manga is an editorial category of Japanese comics targeting an audience of mainly adolescent boys, with the primary target audience defined as either 10 to 19 or 12 to 21 years old. It is the most popular demographic category of manga in the Japanese market. In practice, its actual readership extends to all ages and genders.
Weekly Shōnen Jump was first published in 1968 and has since established itself as the best-selling manga magazine across all demographic categories. As of 2015, its circulation stood at 2,380,000 copies. It has published many of the most commercially successful shōnen series, including Dragon Ball, Naruto, One Piece, Bleach, and Slam Dunk.
Shōnen manga traces its origins to Japanese children's magazines at the turn of the 20th century. Shōnen Sekai, founded in 1895, was Japan's first youth magazine. The first shōnen magazine to publish manga was Shōnen Pakku in 1907, followed by Shōnen Club in 1914.
Osamu Tezuka pioneered the "story manga" format: long-running series with cinematic style and continuity across multiple chapters, contrasting the one-off comic strips that had previously defined the medium. His series Astro Boy and Kimba the White Lion were central works of the post-war shōnen era. Manga Shōnen, one of the first new post-war shōnen magazines, launched in 1947 and published Tezuka's work alongside Leiji Matsumoto and Shōtarō Ishinomori.
At the industry's peak in the mid-1990s, there were 23 shōnen magazines, which collectively sold 662 million copies in 1995. That year, the total manga magazine market consisted of 265 magazines with a combined total of 1.595 billion copies sold.
Shōnen manga focuses primarily on action, adventure, and fighting against monsters or clearly defined forces of evil. Protagonists are typically outsiders who succeed through training, perseverance, and willpower. Rivalry between protagonist and opponent is a central narrative device, and plots generally follow the hero's journey structure, often repeating across multiple story arcs in long-running series.