Wow haven't sizes changed, I was a teenager in the late 60's and the "official" measurements were:
Size 10 - bust 32, waist 22, hip 34
Size 12 - bust 34, waist 24, hip 36
Size 14 - bust 36, waist 26, hip 38.
Just as now lots of girls aspired to be a size 10 - and loads of them were, I was definitely. I would imagine that would be thought of as a rather skinny unhealthy size these days but nearly all my friends were a 10 or 12. Shops didn't stock 6's or 8's as far as I remember and no one had heard of a size zero, mind you, using the sizes above a size zero would be bust 20, waist 10, hip 24 so pretty impossible really!!