Private Sub Worksheet_Change(ByVal Target As Excel.Range)
Application.EnableEvents = False
If Target.Column = 4 Then
  r = Target.Row
   If Cells(r, 4) <> "" Then
     Cells(r, 6) = Int((Now - Cells(r, 4)) / 365.25)
   End If
  End If
Application.EnableEvents = True
End Sub