There are two ways to get the creation date of a file...one using the filesystem object for any file (opened or not) and other is through workbook's buitin properties. Paste the following in a general module of a workbook test run it by running the ExecuteFunc procedure in the same module. Alternatively, you can download the attachment file.

Option Explicit

Function getCreationDate(strCompleteFilePath As String) As Date

    Dim objFileSystem       As Object

    Dim objFile             As Object

    Set objFileSystem = CreateObject("Scripting.FileSystemObject")

    If objFileSystem.FileExists(strCompleteFilePath) Then

        Set objFile = objFileSystem.GetFile(strCompleteFilePath)

        getCreationDate = objFile.DateCreated

    Else

        MsgBox "The specified file '" & strCompleteFilePath & "' does not exist.", vbInformation, "Creation Date"

    End If

    Set objFile = Nothing

End Function

Function getOpnWbkCreationDate(wbkOpened As Workbook) As Date

    getOpnWbkCreationDate = wbkOpened.BuiltinDocumentProperties("Creation Date")

End Function

Sub ExecuteFunc()

    MsgBox getCreationDate(ThisWorkbook.FullName)

    MsgBox getOpnWbkCreationDate(ThisWorkbook)

End Sub