I think there's a distinction to be made with respect to "needing" a user's data in order to be able to provide service at all (for example, a user's age as you

I think there's a distinction to be made with respect to "needing" a user's data in order to be able to provide service at all (for example, a user's age as you cannot permit them to use your application if they're under 13) vs. user data that makes it easier to provide the service, or in your example, advertise your service, to users. If your users are telling you they don't want to give you that data perhaps you should consider listening to them.