I mocked up a form.
a) design view
b) after entering a number of characters.
You may have to adjust your technique, but InputBox is not limited to 5 chars.
Code:
Private Sub Command2_Click()
Dim x As String
Dim ans As String
getlongstring:
10 x = InputBox("enter a string 6 or more characters in the text box", " ") 'InputBox command here============
20 If Len(x) >= 6 Then
30 Else
40 MsgBox "That's only " & Len(x) & " chars -- 6 or more"
50 GoTo getlongstring
60 End If
70 Me.Text0 = Trim(x)
80 ans = MsgBox("great, you entered " & Len(x) & " characters. Do you want to continue", vbYesNo)
90 If ans = vbNo Then Application.Quit
100 GoTo getlongstring
End Sub