I don't think there's anything like gambling experience before one can start gambling, but 18 years and above is a law in most countries these days some young lads boy cut this law because of the introduction of online gambling, some of these platforms don't carry out a proper KYC for their users, you can't start asking gambler how experienced are you before you let them play, it's not a job interview.
It is true that someone who has no experience in gambling is not an experienced gambler in the first place and those who are experienced must have experienced being a beginner before they are finally called experienced gamblers and can handle their gambling. And we also don't know how experienced gamblers start gambling at a young age or when they are already mature. Even since ancient times many young people under 18 have also gambled and most of them gamble with their friends and not on casino platforms which have age limits, especially now that there is online gambling for under 18 years can gamble using their mobile phones.
Indeed, because of the existence of online gamblers, we see a lot of young people gambling because the rules for gamblers in offline casinos only allow 18+, but there is also online gambling which has the same rules, namely by limiting the age, but not all gambling games have that rule if the owner Casinos only think about profits, the most important thing is that the users who play have prepared their money to gamble on their site so it doesn't matter to the casino itself.