Americans liked old prostitutes

I've recently been reading several books about historical prostitution (Dangerous Pleasures by Gail Hershatter, about prostitution in 20th Century Shanghai, mostly focused on pre-Communist Takeover, and Gold Diggers and Silver Miners by Marion Goldman, on 19th Century prostitutes in Virginia City, Nevada, during the silver boom).

Of course there are many similarities between prostitutes from these very different societies: prostitutes are social outcasts, their lives are often miserable and usually end badly, the division between "respectable" women and prostitutes was not always so clear-cut, etc. The fact that has struck me most so far, though, is the age difference between the two societies' prostitutes.

For the Americans, only 6% of prostitutes are under 18 (even though the age of consent in Nevada was 14 and thus a prostitute of 16, say, would be perfectly legal). Even more surprising, 25% of prostitutes are over 35 (which at a time when average life expectancy was 40 is relatively older than it would be today). Many of the high-class prostitutes were in their thirties. In China, all of the relatively high-class prostitutes were under 20 (the average reported age was 16!) and a woman was considered "aging" and washed up if she was between 20-30.

Apparently the Chinese preferred very young girls, while Americans didn't mind aging women: in fact, they often commanded a higher price. I find this strange and unexpected (and have no idea why it is so).