The younger woman thing- How much do you think that stereotype is driven by male desire and how much do you believe is driven by female expectations?

I am an unattached man in his early forties. I work with several attractive women in their early forties and thirties. I also work with some lovely women in their fifties.

When I talk with older women, they seem to wonder why I have not asked out very young women in their early thirties I am friendly with, and encourage me to do so. No one has suggested I ask out the women in my own age bracket.

When I talk to female friends my own age, they tell me younger men have hit on them, but they want want somebody with more experience.

I read articles on websites that indicate men should want women their own age, but everything I experience tells me that is not what women want. Who is driving the younger woman thing?