The maturity age in most of the countries is 18+. So if you can't vote at below 18, you aren't legally adult and hence, bank won't give you loans, you aren't allowed to drink alcohol, and no gambling. Why? Because since under 18 means kid, no one can sue a kid or take an agreement from them. Hence, there's no casino that would allow you to play under 18. Now, I have seen lots of under 18 people singing up on casino by checking "I am over 18" tick box which is really very bad. Because if the casino gets to know it, they will ban you confiscating all your money!