Proof of service or birth certificate still cannot ensure that the person sitting behind the PC and playing gambling is an adult. For instance, if parents want they can provide all this kyc stuff and then give their children access to their screen/PC to gamble. In this case, you can still not avoid minors from playing gambling.
The only way to stop them is to force them to turn on their camera while playing, but why casinos take this hassle when parents themselves allow kids to play gambling.
Everything can be faked out if you wants to do it and bypassing these KYC norms is not much difficult but the thing is they have set a rule at their end to avoid minors falling into this gambling addiction trap but it's the guardian moral responsibility to have look on activities of their children and guide them to avoid gambling at this age instead of helping them in faking out things.
Honestly, would it worth it though? Like I could find KYC information of someone online, buy it from hackers or something and do something illegal there. Then I can use that to sign up here and give that information, which would be illegal as well. And then I could do something legal or illegal here as well and get caught, then all of the money would be stuck inside, what's the point?
This is why I disagree with the situation, getting fake KYC is of course possible, but the possible outcome is so dangerous that you wouldn't want to do it yourself. Not only you could get sued, but you would also lose all of your money at the same time as well.