I'm not sure porn is so much against older performers as it is consumed by the search for the next new thing. Obviously, more 18 year olds give porn a try than 30 year olds and, unless she's one of the lucky few with a huge and very vocal following, the chances of a female making over 100 movies are pretty slim. That's only a couple of years worth of work.
As for older women being more enthusiastic, aside from the fact that women don't reach their sexual peak until they are in their thirties, they are also bound to become more self-confident and assured about their sexual behavior as they gain experience in life. Having watched India and Bamboo for a number of years now I can definitely see the difference.
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