cmon...12 year olds know better than 5 years or younger besides hes a pre-teen. If he doesnt like getting hurt then he should understand that people especially animals dont like getting hurt either.
What Jillio's saying is true, people's brains are not fully developed until they reach adulthood. However, it is true that children by the age of 12 are often taught to understand what's right and what's wrong. However, it doesn't always turn out like that due to underlying psychological conditions.