Hour-based automatic emails

As an organization, certain changes are made to volunteers' eligibility based on how many hours they've earned with our organizaiton. We're hoping to be able to notify volunteers automatically with an email based on hitting a certain level of hours (20). We're also hoping to say congratulations for hitting hour milestones.

We also have age-based eligibility, so an automatic email based on birthday would also be awesome. We allow volunteers 12 years and older to volunteer by themselves, so to be able to notify them with an automatic email on their 12th birthday that they're now eligable for that would be amazing.