There was a Mana Sakura video a while back that showed her with a bunch of ojisan - it made me laugh. One of the scenes was with some 60 or 70 year old guy who was smaller than she was, and she's tiny. He was fascinated by her tits - I was thinking the dude had never been with a Japanese woman that had more than a handful.
Generally, I think the aging of Japan is creating a bigger demand for 'mature' porn, and also providing more supply of porn stars. Or at least, there's less of a supply of younger stars.