Have you known that there is an age restriction in gambling? But it is varied among the countries in the world. I have just checked in wikipedia that commonly someone can play gambling starting from the age of 15/16/18/19/20/21 years. It depends on where he lives, every country may have different regulation related to the age restriction. Below I classify some countries based on the age restriction:

Age 5: Malawi (Casino)

Age 15: Iceland (lottery)

Age 16: United Kingdom (Football pool, Scratchcards), Estonia (other), New Zealand (instant kiwi)

Age 18: Australia, Kiribati, Nauru, New Zealand (horse racing), Palau, Solomon Islands, Tuvalu, Vanuatu, Vanuatu, Albania, Austria, Belarus, Bulgaria, Croatia, Czech Republic, Denmark, Faroe Islands, Finland, France, Germany, Gibraltar, etc

Age 19: South Korea, Canada, USA

Age 20: New Zealand (Casino), Sweden (Casino), Japan, Nigeria

Age 21: Belgium, Estonia (Casino), Armenia, India, Lebanon, Macau, Malaysia, Philippines (casino), Singapore, Taiwan, Vietnam, Cote d'Ivoire, Egypt, Namibia, Niger (casino), Bahamas, Saint Kitts and Nevis, US Virgin Islands (casino), USA, Macau

Age 23: Greece

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Source & more detail information: https://en.wikipedia.org/wiki/Gambling_age#cite_note-27