I don't think this rating is meaningful on the Internet, because games can be downloaded and purchased at will. It can't verify what age people or children bought adult or pornographic content.
If it is a physical CD, the seller can verify the age of the other party (only need to submit the ID card).
In addition, I think that if there is too much adult content, this website will be blocked by many countries because it violates the minor protection law.
The best way is to lock the areas that do not accept porn so that they cannot access pornographic content. Only 16+(or less) content is open to these countries.
That's what STEAM does.