In response to shifting demographics, MTV announced a major change in the station's format Monday. Older-audience favorites such as Art Nunckmueller's Bass Fishing All Stars and Ballroom Memories, formerly the cornerstone of MTV's programming, will be replaced by programs geared toward a younger audience. 'We believe the over-50 market has been saturated by cable TV,' MTV head of programming Stan Goldberg said. 'It's high time someone offered programming for the 17 to 24 crowd.' Some of the new shows planned include reruns of Dick Clark's American Bandstand and Christian Teen Talk with Father Ben Kendall. 