That's not how that responsibility works casinos can't allow a twelve year old to gamble because they show'd up with an ID from a 25 year old. Online gambling is already questionable in the US, allowing underage gambling would be the nail in the coffin. You might not, others, particularly gambling addicts might think otherwise. If Port wasn't selling gold in the form of COTOs and endorsing people to buy and sell those COTOs for real world money, they'd probably be fine, but since they are any gambling in game is close enough to the real thing for the government to take notice. The "just a game" bit already falls flat some places, Japan has consistent issues with folks using pachinko parlors to gamble by proxy, can't see how this would be treated differently.