From the study of Krinkle, given by Tanvir vai; it is found that the oldest edit made by a person is on 26 December 2003. And the oldest revision that is still visible on Bengali Wikipedia today is on 27 January 2004. And still there are other older edits made by developer as placeholder page (on 1 June 2002) and language code subdomain (on February 2002), which are solely for technical purpose. Therefore 26 December 2003 seems to be the date when a person made an edit to the Main Page (then HomePage).