For countries where gambling has legal status, I think they have an age limit that is allowed to gamble and of course most of them are physical gambling companies. For online gambling, I think smart kids can gamble even though the site has warned about player age limit. There are loopholes where children can gamble online even in countries where gambling is prohibited.

I found many children under 18 who were very good at betting on sports gambling and Lotteries at my place. So even though there is an age limit then if its online gambling it will be difficult to prevent. KYC will not be accepted by many gambler because it is related to the privacy security of player, we can move to other site if we do not want to deal with KYC document.