I was thinking around 1959, the year the high school girls came back from Christmas break wearing sack dresses.
The late '50s and '60s BEFORE '68, were also the years of what is now called the PREPPY look...which was VERY 1920s for both sexes! And boys, in prep school, who were Seniors were quite pipe smokers.
The high school girls were still wearing hose and garters.