Play's Age Signals terms limit the signal to age-appropriate experiences and name advertising, marketing, profiling and analytics as prohibited uses, with app takedown as the stated penalty. Apple's version hands you the age plus how it was proven. Both are live now in a widening list of regions, and the default engineering reflex is wrong for both.
There's a new field arriving in mobile apps this year and almost nobody is treating it as a product decision. It's the user's age, handed to you by the store instead of asked for in your onboarding.