Error with Type Mismatch

Hey there, I am trying to check a user input to see if the user has entered the date correctly.

I am using the code below but it keeps giving me a "Type Mismatch" error. Does anyone know where I am going wrong?

Sub remove_old_data()

Dim dateDim As String

Do While (date_check(dateDim) = 1)

    dateDim = InputBox(Prompt:="Please enter the date you wish to filter from: ", _
          Title:="Date Filter", Default:="Date filter")
Loop

End Sub


Function date_check(datePar As String)

If (Format(datePar) <> Format(CDate(datePar), "DD/MM/YYYY")) Then 'checks if the format of the cell is equivalent to "DD/MM/YYYY", as required for import
        MsgBox "Please enter the date in the format ""DD/MM/YYYY"".", vbInformation, "Remove Old Data"
        'highlights in which cell the error took place
        date_check = 1                      'returns a 1 to indicate an error has occured
        Exit Function                       'exits the function
    Else
        date_check = 0
    End If
    
End Function

Any help would be greatly appreciated, thanks.

Jag