It's not enough to just accept the age signal:

> (3) (A) Except as provided in subparagraph (B), a developer shall treat a signal received pursuant to this title as the primary indicator of a user’s age range for purposes of determining the user’s age.

> (B) If a developer has internal clear and convincing information that a user’s age is different than the age indicated by a signal received pursuant to this title, the developer shall use that information as the primary indicator of the user’s age.

Developers are still liable if they have reason to believe someone is underage, even if the age signal says otherwise.

The only way to truly minimize that liability is forcing users to scan their faces and IDs, that is why age verification systems are already implemented that way.