I just tweeted something about Amsterdam smelling like piss when I was there, then I realized that I haven't been there in TWENTY FUCKING YEARS. I quickly tweeted a retraction. I'm not qualified to have any opinions about Amsterdam. Other than the old landmarks and general geography, I don't know shit about that city.

So, how many years have to pass before your knowledge of a city becomes completely outdated. I'd say 10 under normal circumstances and 3-5 in cities with hypergentrification.