Enter current date into a TextBox

I have a GridView with a a string date field in the format of YYYMMMDDD, ie 21010218, I can filter the 3000 records very quickly by entering the current date, 20100218, into the TextBox by clicking on a Submit Button. How can I automate this process by automatically entering the current date into the TextBox so that the filtering will always show all records that have a date older than the current date?