Generally it is legal to play in the casino if you have reached the age of 18, that may vary from country to country.  

It is only obviously legal to play in a legal online casino or a casino which has in possession of a regular license to exert gambling.   

If you are of age you will be able in fact to go in a real casino, and you can also play in the online casino.   

Some states with a conservative and antiquated culture as for example Italy and China have recently adopted some high restrictive measures to darken the sites of bets and the online casino, showing them as illegal without a right minded motive. The only aim of this action would seem really the guardianship of their own state of monopoly towards gambling.   

Fortunately for the customers a working method exists to stop the block of the aams.