Although many studies have been done, nothing has been proven. I don't see companies marketing viagra to 40 something women, so I think that speaks volumes.
I will agree that some older men may be more attractive to a young woman looking for security. However, there is also a trend for younger men to be seeking older women.
That's because older women are a "sure thing." Guys don't have to put forth much effort to get in their pants, because for the most part, older women are desparate.