I've been seeing age checks like this more and more. Recently the FTC came down hard[0] on Kurbo (aka Weight Watchers) for not doing enough/anything to stop children under 13 (COPPA) from making accounts. Since they're not confident there's no children with accounts, now all Kurbo's data is tainted and they have to delete all user data and destroy any "algorithms" derived from that data. Historically Dropbox probably…
"the agency... marketed a weight loss app for use by children as young as eight and then collected their personal information without parental permission."
That is pretty wilful -- so we can be confident they have or had data targeted from children. Dropbox on the other hand -- I'm not sure how that case is similar. Are children now allowed to use cloud backup services? Why wouldn't they?