This is a very good step. It would prevent minors from being unnecessarily exposed to gambling since you'll be made to verify yourself before being allowed to gamble.
What about people who look younger than they are? For example an actor Thomas Brodie-Sangster. Take a look on this picture:

In 2009 he was already 19, but he looked like a someone who just got graduated to middle school. I am 100% sure that casino security would not allow him to gamble, even though is an adult. Here is another example, Dwayne "The Rock Johnson" at age of 15.

He can easily pass selfie requirement or even visit offline casino without asking for ID. That selfie requirement has more disadvantages than advantages.