SHOW: THE COSBY SHOW
TIME: THURSDAY, APRIL 30, 8 P.M. EDT, NBC, FOR THE LAST TIME
THE BOTTOM LINE: The most successful sitcom of the '80s makes a graceful exit.
Nothing on TV ages faster than a family show. The regulars at the Cheers bar or the M*A*S*H unit can stick around for years, with only occasional cast changes to accommodate stars who want to get into movies. But kids have a bad habit of growing up. Anyone tuning in after a few years' absence to this week's final episode of The Cosby Show may get a shock. Theo (Malcolm-Jamal Warner),...