I think it depends upon the environment/upbringing of the person and his tenacity to play around with a highly speculative game. I've known some kids here in our country (Philippines) as young as 12-13 years old to gamble against adults, especially those who were born in the slum areas. They are usually children of gamblers as well, and they learn at an early age how to play against the psychology of an adult in a game in order to earn a bit of cash.
Well, that's illegal of course, and that's not a perfect age bracket for someone to gamble. For sure these kids are doing illegal stuff as well like stealing money from their parents or worse from another person.
I have seen children like these as well, and they are stubborn as hell. The least you can do is to report this to the authorities before anything worse will happen.