Vintage ladies 1960's

I found it at an antique shop. The lady said she believes it is from the 1960's. I don't know the size but the measurements are: shoulder across the front from seam to seam is 16 inches. Under the arms from seam to seam across the front is 20.5 inches. It is 38.5 inches long. It is 21 inches across the front of the waist. I assume you double the measurements for the back. I am guessing small. Possibly pettit. I don't know if it was worn but it does have tags.