Feature Change - Add tags create and modified timestamps as tags to azure resources
For an azure resource, the activity logs are available only for 90 days.
Post that there is no way to find out the "Creation Date" for the resource.
Sometimes creation date matters w.r.t availability of features. For eg: All the Cosmos DB instances that have created post a certain date have default partition key size more than 2k bytes. Prior to that the default value was 100 bytes.
Quoting Azure support team
Unless you add a tag with the creation date, the only way to get a creation date is to use Azure Activity Log to search for the creation operation of the resource. These logs are only saved for 90 days, so if the resource was created more than 90 days ago, there is no way to find the creation date.