About 30 minutes before it’s over, Flashback begins to go to pieces, like someone who has overdosed on carrot juice and organic marzipan. The movie becomes woozy and sort of distraught. Until then, it’s an engaging comedy about the confrontation of a superannuated flower child of the 1960s and a 26-year-old representative of the clean-shaven, cholesterol-conscious, fiercely conservative 1980s. — Vincent Canby