For example, compulsory education ends in primary school at the age of ten.
Students are free to continue into middle school if they wish. When children complete primary school at the age of ten, they are legally considered as adults.
This is the “All Primary School Graduates are Adults Law”. Or PGAL (Primary Graduates Adulthood Law) for short.
Basically, as of the April following your tenth birthday... you are able to gain a Pokémon License and are permitted to carry Monster Balls to capture Pokémon.
Of course, there's more to being a legal adult than the right to own Pokémon.
All adult rights are granted. Under 18s don't qualify as minors, not even 14 or 15 year olds. For example, if you were to steal something from a convenience store, the consequences would be more than just the shopkeeper getting mad at you, the police would arrest you. And no matter how much your parents try to apologise, you are still culpable as an adult.
The most important point of this law is... after leaving primary school you make your own life choices.
You can strive to achieve higher education or take over the family business.
Naturally, you're free to search for a job you like as well. If they were so inclined, an eleven year old boy and girl are even free to marry without parental consent. You are considered an adult right down to details like traffic violations. ... And you pay taxes like an adult too.
So, in regards to Satoshi's hometown, Masara Town...
Masara Town is a small town out in the boonies. Despite being legal adults, there's barely any job openings for primary school graduates there.
Due to the lack of jobs, it is a town where most children decide to become Pokémon Trainers.