The creation date is not when the document was created in the application, it's when the file was created.

If you create a new document, then leave it open for a week on your computer before saving it, it will have the creation date when it was saved, not when it was actually created in the application. So, the first time it is saved, it will have the same dates for creation and modification. And as mentioned, the date information is not usually retained when the file is sent via email; the creation date will be the date the attachment was saved, regardless of when the original document was created.