Age ratings and an age gate for 9+ and 12+ apps

Apps now carry a content rating, collected from creators at publish time and independently assessed by an automated screener that caps ratings at 12+. Viewers of a rated app are asked once for their birth year (stored on the account when signed in, or in a private cookie when anonymous) and can't reach content above their age. The gate is enforced on both the page and the data layer, and it never leaks the existence of unpublished or private apps to outsiders.