Why do older women dislike younger women and act more kindly to younger men?

When I was a teen, older women and older men (late 30s- late 50s) at my part-time typist work in a law office/cashiers at grocery stores/etc were polite but indifferent to me. I'm 24 right now. I noticed that older men are much friendlier than before and older women are even less friendly. The older women kind of ignore me and talk with each other. For example, at my new workplace - the teenage girl clerical assistant and men introduced themselves to me with a smile and try to start conversations. But none of the older women ever introduced themselves or talked to me and when I say "hi" they give a disinterested "hi" back then look away, but they talk to each other a lot. If I make a mistake they yell at me (even though they're not my boss, just coworkers) or say something sarcastic but they rarely do that to each other. I have a few friends who have the same experience, but my male friends say they have the opposite experience - that some of them get special treatment.