when the show begins in 1960, opie is six years old and thus his birth occurred in 1954 (the same year in which ron howard, who portrayed him, was born). andy may have married in 1952, the same year he apparently became sheriff. in an episode where barney tries to find andy a wife, andy admits that he misses having a wife to come home to after work. if andy's wife died the year opie was born, they may have been married only two or three years. this could explain why opie was an only child.