In Missouri, you must be at least 21 years old to enter a casino and participate in gambling activities. This age requirement is strictly enforced by state law to prevent underage gambling. Casinos in Missouri may request identification to verify your age before allowing you to enter the premises. It is important to have a valid ID with you if you wish to gamble at a casino in Missouri. Make sure to meet the age requirement before planning a visit to a casino in the state.