I think you have it backwards, perhaps. Prescriptive is like when a doctor tells you what drugs to take via a prescription. That’s the old man one. (Although I think it’s quite often younger people who have recently had the idea of correct and incorrect useages of languages drilled into them!) Oh, either you edited your post, or I’m crazy. :)

Also, while too much prescriptivism is certainly obnoxious, not enough has its own problems. Language needs a certain amount of conformity to ensure were actually having a conversation about what we both think we’re having a conversation about.