AR Invoice

We would like to restrict users entering the AR invoice through Standard Invoice entry program P03B11 from entering old invoice dates on the screen in 9.1. From what I know the only aspects that are checked by system are whether the invoice date is greater than today's date or greater than GL date by there arent any checks on the old invoice date. I would like to confirm if anyone can advice how to restrict user from entering invoice date which is older than current period or so...

While I know Invoice date defaults to GL date if left blank however its possible user may enter incorrect past invoice date.