Its not about maturity.
Maturity only factors into the equation slightly. Its about liability and in Canada the age where one can be legally held responsible for their actions is the age of 18. Given the nature of airsoft and how the the devices look if something were to go wrong or they were to be misused the only person to blame and be held responsible would be the person who was using them and not their parent or guardian.
"Its only a little bit on fire"