If any minor uses his adult friend/cousin/relative to pass the KYC, this is morally not correct. Although the gambling site may not be able to trace it but it is not good for the minors to play gambling. They are not mature and can misuse the funds of their family.
I concluded that the KYC procedure is necessary, although I personally do not like it.
No it should not be nessesary because as mentioned in above post, the minors can use the adult identity and bypass the age restrictions, so it is bogus to implement KYC to control the minors accessing the sites. The parents/ guardians of minor need to be more responsible and keep an eye on their children activities