You have to be at least 21 years old to enter a casino in most states in the United States. This age requirement is strictly enforced to ensure compliance with gambling regulations. Minors are not allowed on the gaming floor or to participate in any form of gambling. Casinos typically check identification to verify the age of patrons before allowing them to enter. It is important to have a valid government-issued ID with you when visiting a casino to avoid any issues. Remember to always gamble responsibly and within your means.