[SalesForce] Workflow rule on opportunity to check account status (custom field) and update opportunity field status

Since you are trying to update a parent record based on the entire group of related child records it seems to me you will need to use a query inside of an apex class or trigger.

The way I would likely go about solving this would be to put a trigger on the opportunity object. Any time an opportunity is inserted or updated with a different status you will need to add the parent account ID to a set. After all your trigger logic fires, you will need to query all opps related to any parent account in your set and loop through all of the opp statuses like Maneesh said.

There may be some way to muscle in a solution using workflows or rollups, but anytime you are trying to do logic with a group of child records I have found that code and a query is required.

You are using a formula field. Formula field is not stored in database and are evaluated at run time.

1. As workflow rule fire only when there is change in data create/edit. As change in formula field is not excatly change in data as its not a field in database, thus the workflow wont fire automatically when Applicant reaches a certain age.
2. When you edit that record, then workflow rule fires and evalutes the criteria. During evaluation it finds that formula value has changed and should trigger a field update.
3. subsequently met criteria only fires when old value is different than new value. So before DML the formula value and after dmL formula value is same, it wont trigger the field update.

You have to use Scheduler/Time Based workflow for this behavior.

Below link mentions both approches to send email via Scheduler and via time based workflow. http://www.simplysfdc.com/2015/02/salesforce-send-birthday-email.html