Eh, I don't buy it. I think you had a couple of experiences you didn't really like with "older women" aka women your own age and decided you like young, nubile things that will do what you tell them to.
Sex is highly personalized and depends on chemistry and personality. I've had great sex with older guys and younger guys, and horrible sex with older guys and younger guys. In the grand scheme of things, even with a number higher than at least 75% of people, my sample size isn't enough to draw conclusions from.
Things like flexibility are partially a function of where people are in life. Yeah, a 40 year old is going to be more likely to have job and family commitments that get in the way of spontaneity. That doesn't make her worse at sex.