20 years isn't that broad. It's the commonly accepted meaning for "generation".
As someone who did high school just slightly before social networks became an obligation, I don't really feel that way towards anybody less than 20ish right now. Suppose in 15 years (hypothetically) I'm faced with my own kids entering social media, I will have no personal experience to base my parenting on. In any case, the dictionary definition for generation is pretty much the age at which people become parents, which tends to be anywhere between 25 and 33 these days.
As for OP, amusing. The 70 years older joke is hofstadterially comical. This even manages to be close to a fateful image of the generation, at times.