You have to remember, if kids are bored, they would spend hours on their phones or playing console games or even watching
TV. Adults on the other hand, will use gambling as a way of entertainment and to burn some time. (Yes, some adults still
play games) The difference between kids and adult games is the money they win or lose on gambling.
IMO such a separation relating to different entertainment based on the age isn't exactly accurate. I think this is more about an environment, hormones and individual needs, maybe even genes determine craving for certain games (there was even a study about that https://www.bionews.org.uk/page_91056), as there are adults, that are okay with watching TV, news and alike - it's their amusement, on the other hand there are kids that would prefer playing hazardous games, cards, where they can feel the sweetness of victory. Take Monopoly, for instance - a typical game which proves that from the very childhood kids want to play games that involve money and power. I bet some schoolboys would enjoy playing poker if they knew the rules and would've bet everything they owned.