In the 1980s and 1990s, "oldies" meant the 15 years from the birth of rock n roll to the beginning of the singer-songwriter era of the early 1970s, or about 1955 to 1972, although this varied and some radio stations chose 1950–1969. Whatever you label it as, it will always be "Oldies but Goodies" to me.
Here are some prime examples of what I'm talking about.