Klar, so:

Option Explicit
 
Public Sub sort_groups()
    Dim l As Long, z As Long
    Dim iColGrp As Integer, iColSort As Integer, iColOut As Integer, tmp As Integer
    Dim wks As Worksheet
     
    l = 2                               'Zeile, in der begonnen wird, bei Tabellen mit Überschrift = 2
    iColGrp = 1                         'Spalte, in der die Gruppe steht (Ganzzahliger Wert)
    iColSort = 2                        'Spalte, in der das Sortierkriterium steht (Ganzzahliger Wert)
    iColOut = 3                         'Spalte, in der die Markierung gesetzt werden soll (Ganzzahliger Wert)
    Set wks = Worksheets("Tabelle1")    'Tabelle, die bearbeitet werden soll
     
    With wks
        Do While .Cells(l, iColGrp) <> vbNullString And .Cells(l, iColSort) <> vbNullString
            tmp = CInt(.Cells(l, iColSort))
            z = l
            Do While .Cells(z, iColGrp) = .Cells(l, iColGrp)
                If .Cells(z, iColSort) > tmp Then
                    tmp = .Cells(z, iColSort)
                End If
                z = z + 1
            Loop
            Call mark_max_group_sort(l, wks, iColGrp, iColSort, CStr(.Cells(l, iColGrp) & tmp), iColOut)
            l = z
            l = l + 1
        Loop
    End With
    
    Set wks = Nothing
End Sub
 
Private Sub mark_max_group_sort(ByVal l As Long, ByRef wks As Worksheet, ByVal iColGrp As Integer, ByVal iColSort As Integer, ByVal sKey As String, iColOut As Integer)
    Dim tmp As String
     
    With wks
        Do While Not .Cells(l, iColGrp) = vbNullString
            tmp = .Cells(l, iColGrp) & .Cells(l, iColSort)
            If tmp = sKey Then
                '.Cells(l, iColOut) = "MAX"
                .Cells(l, iColSort).Interior.Color = RGB(255, 0, 0)
                Exit Sub
            End If
            l = l + 1
        Loop
    End With
     
    MsgBox "Schlüssel " & sKey & " nicht gefunden..", vbInformation
End Sub

Gruß