Here is what I came up with that seems to be working:

Dim ArchiveDate As Date
Dim LastRow as Long
'Calculate date to delete rows, E25=This week saturday date,
J16=Number of weeks to go back
ArchiveDate = ThisWorkbook.Sheets("Settings").Range("E25").Value - _
(ThisWorkbook.Sheets("Settings").Range("J16").Valu e * 7)
LastRow = Sheets("Archive").Cells(Sheets("Archive").Rows.Cou nt,
"A").End(xlUp).Row + 1
With Sheets("Archive")
'Data starts at row 6
Do While LastRow 5
If .Range("A" & LastRow).NumberFormat = "d-mmm-yy" Then
If .Range("A" & LastRow).Value <= ArchiveDate Then
MsgBox ("Got a hit")
Rows(LastRow).Delete
End If
End If
LastRow = LastRow - 1
Loop
End With

What do you think?

Thanks for the sugestion to comapre the format, that is the answer to
this problem.
Cheers.