A recent article at the Metro Trends blog, unfortunately, seems to have conflated youth with gentrification, and in the process even managed to confuse the meaning of the word "revitalization."
Their case, essentially, is that cities are attracting young, educated 20-35 year-olds—people from the Millennial generation—but maybe it's not as much as we all like to think. That's debatable, but then they go on to say that what is increasing by a lot is college-educated adults, as if that's some kind of revelation, and evidence that gentrification isn't happening as much as we all think.
It's hard to even explain how confused they are about what gentrification is without reproducing the whole article, so I recommend you take 3 minutes to read it. Because of how they rewrote the article after discovering a flaw in their data, it's hard to tease out their conclusion, but what does seem clear is that they're using in-migration of hipsters and young professionals, "gentrification," and "revitalization" as basically interchangeable terms.
So let's just clear things up. First, some good old Oxford English Dictionary definitions:
Gentrify: To renovate or convert (housing, esp. in an inner-city area) so that it conforms to middle-class taste; to render (an area) middle-class.
Gentry: (1) Rank by birth (usually, high birth; rarely in neutral sense); (2) People of gentle birth and breeding; the class to which they belong; in modern English use spec. the class immediately below the nobility.
To be a member of the gentry, in the archaic use of the word, is to be of high social ranking, but not quite among the elite of society. In the modern sense, to gentrify is to convert an area to a higher economic (and therefore social) class and character. The specific definition refers to a conversion to middle class tastes, but I think it's fair to say that the meaning of the word has evolved to include any such conversion: low to middle class, middle to upper class, whatever.
Notice that this says nothing about a person's age. Gentrification is about wealth and social class, not age. Whether the affluent person moving into San Francisco and displacing long-time, lower-income residents is 25 or 55 years old, that's still gentrification. (And to be clear, the new resident has every right to move where they like, if they can afford to do so -- it's government's responsibility to accommodate enough growth to provide new residents housing while limiting displacement.)
People talk so much about gentrification and Millennials that it seems they've started to mean the same thing to some people, and now even a completely benign word like "revitalization" is being demonized. If nothing else I think this just demonstrates how little people really understand about the connection between housing supply and demand, affordability, and demographics. If we can't even keep our buzz words straight we've got a long way to go toward finding a solution.