At present, the first thing a website which processes the data of its users (whether or not they open an account or actively submit any personal information) and offers access to content which may be deemed harmful to children, should at least apply a check that all its users are 18 or over.
Checks at 13 are also being developed, primarily for Social Media – see FAQ’s below.
In time, more granular checks for younger children may become available, but for now, the safest policy to ensure compliance with UK law is to apply an adult age check to prevent access to any material harmful to children.