In 1962 I was 18 years old -- a super-active, skinny (sort of scrawny, actually) kid -- weighed perhaps 120 (we didn't own a scale, you got weighed at the doctor's for physicals -- with shoes on and mid-day) -- and I wore a size 12! (I'm 5'7")

Remember those days? -- elastic was kind of iffy (I remember a pair of panties falling off me on the way to church one morning -- super embarrassing moment -- must have been around 13-14 years old) and stockings with garter belts (that would "pop" up when you sat down (again, at church -- you didn't afford stockings for other times)....

So yes (in spite of my rambling) sizes have changed over the years -- right now I typically wear a 10 (and I weigh 152) and I am nowhere near the physical condition that I was in back then.....