WIP issue-358 COPPA fix

Need to add validation and tidy things up. Also, maybe i should split all of this into a mixin?
Maybe invert the if clause for clarity:
```js
// Only check the month/day in the cutoff year. 
if (userAge.year === CUTOFF_AGE.year) {
  return this._validateYear() && this._validateMonthAndDate();
}
// validateYear will take care of users that are too young.
return this._validateYear();
```