After reading through the forums for some time with no luck, I finally found a way to automatically recalculate a contacts age in Zoho CRM.

First, I added a custom field as a Single Line field called Last Auto Update

Then, I added a function to the contact layout with the following formula to calculate age:

Floor(Datecomp(Now(),${Contacts.Date of Birth})/(60*24*365.2425))

Next I created a workflow that triggered on Birthday that notifies me via Slack when I birthday occurs and also performs a field update function.

The field update function updates the Last Auto Update field with the variable ${EXECUTION_DATE}

This is REALLY kludgy but it works.  All the other solutions I found online either required custom modules (which I tried and didn't seem to work) or just didn't work at all.  If anyone has a more elegant solution, please let me know.