Creating an awareness about it is very important but limiting exposure is also a very significant step in keeping them away from it. There are a lot of things that the society educates young people to be careful of but they still end up doing those things because there are no restrictions or limits. If every gambling center of casinos can strictly adhere to the rule of not allowing underage to gamble it would make the society a better place. It's actually very concerning to see teenagers under the age of 17 playing sport virtuals, this can affect their mentality.
The casino already shared enough warning that gambling is not for minors. Anyone who is below the age of 18 is not supposed to be allowed to gamble by regulations that are publicly made known to gamblers, but those kids who still want to gamble will do just that, and it's even harder to stop them from entering a physical gambling shop because of growth.
You can see a child who is not up to 18 years old looking all grown up like someone who is in their early twenties. How can you stop such people? You and I can agree that it's not possible to be asking for each customer's ID card before you allow them to place a bet.
Are you talking about offline gambling? If yes, then if you can check every customers ID before placing a bet (if you can evaluate his age by looking on him), then such casino should stop operating. Its not possible or impossible to check, its a duty to check age. As to online gambling, then yes, its totally impossible to check everyones ID. In fact, rare online casino try to check ID during registration. They usually allow everyone to register freely.