If the main intention is to prevent under-age players from participating in gambling, then I would say that KYC will be having hardly any impact. I have seen kids as young as 12 years using the Tor browser in my city. Don't you think that they will be tempted to use illegal gambling sites (where KYC is not required) in case the legal ones ask for KYC?
Kids like that are the main reason why it has become a thing of necessity for all sites to have KYC regulation. Dont worry, its just a matter of time and I believe it would become mandatory for all genuine site and every gambler would have no choice than to adapt too this and for those who still find it difficult, they might be left between the option of either obeying or going to play on scam sites while they stand the risk of losing their money.
For those minors, by the time there is 100% compliance of all sites asking for KYC before license, they would have to wait till they are of gambling age or otherwise go to play on scam sites and lose all their money.