Private Sub TextBox1_Exit(ByVal Cancel As MSForms.ReturnBoolean)
Dim an, mois
an = Year(Date) '2019 'à adapter
mois = Month(Date) '8 'à adater
With TextBox1
If Not IsDate(.Text) Then .Text = "": Cancel = True: Exit Sub
If CDate(.Text) < DateSerial(an, mois, 1) Then .Text = "": Cancel = True: Exit Sub
.Text = Format(.Text, "dd/mm/yyyy")
End With
End Sub