Getting a list of VNETs in a Resource Group is easy. You can do that in the portal by selecting a Resource Group, and then setting 'type' equal to 'Virtual Networks'
You can do this in PowerShell using the Get-AzVirtualNetwork cmdlet and specify a Resource Group.
what is MUCH harder about this question, is sorting by creation date. Azure does not save the creation date on your resource. 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.