As a geezer, I often use the word "whippersnapper". To me it means someone younger than I who is less serious and more assertive than I. It's definitely ageist, (Ageism is perhaps the one dichotomy which will last the longest. We've seen race and sex and gender being dissolved away, distinctions fading, epithets being outlawed.) But everyone is young and everyone will be old. Only if we finally conquer death will the distinctions between the generations fade away.)
Today I wonder about its origin. Google shows that the origin is fuzzy, perhaps from "whip snapper". However a British site says it's a combination in the 17th century of "whip snapper" and "snipper snapper". From meaning a street boy who had no ambition but lazily snapping a whip for recreation it came to mean "A diminutive or insignificant person, especially a sprightly or impertinent youngster" in the sites definition.