This seems to be an opt-in, user-supplied field that apps can use to implement parental controls easier. If you're gonna do birth dates at all, this is the way.
But IMO it should be more granular: there should be fields for WWW access, social media access, sex/nudity/violent content, and apps should respect those individually. Then parents can choose what is appropriate for their child at their development level.
Sorry to be picky, but it's definitely way more than 40000 dead Palestinians.