[APP-615] COPPA-compliant signup (#570)

* Rework account creation to be COPPA compliant

* Fix lint

* Switch android datepicker to use the spinner mode

* Fix type signatures & usages

src/lib/strings/time.ts

@@ -39,3 +39,13 @@ export function niceDate(date: number | string | Date) {
     minute: '2-digit',
   })}`
 }
+
+export function getAge(birthDate: Date): number {
+  var today = new Date()
+  var age = today.getFullYear() - birthDate.getFullYear()
+  var m = today.getMonth() - birthDate.getMonth()
+  if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
+    age--
+  }
+  return age
+}