Setting the age rating for a game will prevent an underage user from being able to access it. The date of birth of the user in registration will allow the games/apps manager in web admin to determine if the user is not allowed to see the game.
-Go to Settings > Client configuration > Games/Apps.
-Search for the game where you want to set an age restriction.
-Click on the game to see its details, then set the age in "Age rating" field.
-Once done editing, click the "Save" button. Be sure to restart the client PCs to apply the changes.