Reg Database

I don't think you can check it inside NAV.

You can however check this sort of things in SQL Server Management Studio - right click on the database, click Properties, and in General tab you will see the Database Created property. That would be when the database has been restored.

Ask the server/database administrator?

You can retrieve creation date by executing the following T-SQL query against your SQL Server

SELECT create_date
FROM sys.databases
WHERE name = 'MyDatabaseName'

Any tool which will let you connect to the database and let you execute the query above will do.

You could even build something in NAV enabling you to run T-SQL queries and retrieve results from any database. It is a bit complicated, but if you look into UpgradeToolkit on the installation DVD there is a codeunit inside one of these fobs, Upgrade - SQL Mgt, which will have all DotNET components already defined, and also a code base you can learn from.