Biometric identification technology is indeed very effective, the system detects it in just seconds, I haven't heard of anyone who can fool the system. Too many gambling sites and minors will definitely find other solutions so they can gamble, the most to be considered is their connection and the role of parents who should monitor whither they access website, restrictions that must be increased.
Biometrics also has its exploits, not unless you're using retina or iris scanners for identification, but that technology in itself is extremely expensive and I doubt that your local law enforcement, or any other organization for that matter, will use it just to curb minors away from gambling. Ever heard of
one guy recreating a politician's fingerprint from just mere pictures? Biometrics is a promising field for security enforcement, but it has a long way to go for it to be tightly secure.