What actions will cause a domain age value to reset to 0?
The obvious action is a domain registration which would set the domain age to 0.
What about a domain transfer (from one registrar to another), does that reset the domain age to 0 in UltraDDR?
Domain age is based off of the created date. In the scenario where a domain is transferred from one registrar to another, the domain age is calculated based on the difference between the domain created date and today's current date, which could be 0.