From Bulbapedia, the community-driven Pokémon encyclopedia.
A Pokémon Trainer's license, also known as a Pokémon handler's license or simply a Pokémon license, gives the bearer the right to own Pokémon.
In the anime, applicants must be 10 years of age or older.
In the games
According to the blurbs of Pokémon Red, Blue, and Yellow, Red obtained his Pokémon Trainer's license and has set out to become a Pokémon Master.
In Pokémon Sun, Moon, Ultra Sun, and Ultra Moon, it is revealed that Trainers in the Alola region may only take on the island challenge when they turn 11.
In the anime
In Pokémon - I Choose You!, Ash was excited that he could get his Pokémon license now that he was ten years old. In The Battling Eevee Brothers, Rainer tells Mikey that he could lose his "Trainer qualification" for leaving his Eevee alone and tied to a tree.
However, despite the case of Ash or other characters such as Max and Bonnie, who were specifically stated to be too young to have their own Pokémon, children under the age of ten have been shown to own Pokémon. It is generally an accepted fandom theory that minors under the age of ten may own Pokémon, but are not allowed to compete in official tournaments hosted by the League Competition Committee and the Pokémon Activities Committee, which include the Pokémon League Conference and the Grand Festival.
In the manga
In The Electric Tale of Pikachu manga
According to The Electric Tale of Pikachu manga, potential Trainers are required to attend a half-day training session before qualifying to take a brief test. Those who pass the examination receive the license. Only licensed Trainers are legally allowed to purchase Poké Balls.
In other languages