This is said to be from a 1943 issue of Transportation Magazine:
1. Pick young married women. They usually have more of a sense of responsibility than their unmarried sisters, they’re less likely to be flirtatious, they need the work or they wouldn’t be doing it, they still have the pep and interest to work hard and to deal with the public efficiently.
2. When you have to use older women, try to get ones who have worked outside the home at some time in their lives. Older women who have never contacted the public have a hard time adapting themselves and are inclined to be cantankerous and fussy. It’s always well to impress upon older women the importance of friendliness and courtesy.
3. General experience indicates that “husky” girls – those who are just a little on the heavy side – are more even tempered and efficient than their underweight sisters.
Snopes has this as true.