My reading of 2A is that devs can take the word of the OS or App Store. If they say the user’s 18, and the user’s really 13, then the developer’s in the clear for serving adult content to them because they took the word of the certifying entity.

Conversely, if the OS says the user’s 13, then they can’t say they thought the user was actually 18. Guess sucks to suck if you want to buy a movie ticket from your kid’s phone, or if you mistyped your age when you set yours up because you didn’t have your passport nearby.