Restrict Proposed Start Date to Current or Future Date Only

Summary:

We are trying to restrict the user from entering a past date for the 'Proposed Start Date' in the When and Why page of Add a Pending Worker.

Ideally this would grey out the past dates on the calendar but we would also accept an error validation.

We are currently trying to set up a validation error using the below code (Unsuccessfully) -

Any suggestion would be gratefully received.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

25B

Code Snippet (add any code snippets that support your topic, if applicable):