Plenty of elderly in the Netherlands biking around too. Are they also an outlier?

I mean, they kind of are, but only in the sense that they have a ton of good bike infrastructure. If we built bike infrastructure that well, we also could have elderly cyclists.

They also have very flat land and an amenable climate in the Netherlands.

Cycling becomes significantly harder in hilly or windy (read coastal) locations.

I live somewhere generally considered "flat" as there are no mountains, however there are a lot of undulations (short, steep hills) and a Mediterranean climate (hot, dry summers) with strong, coastal winds in the morning and afternoon. Cycling any distance in summer will involve sweating. Most people opt to drive in an air-conditioned car, even the 1 km to get some milk/bread.

Better/more bike infrastructure is unlikely to change most peoples behavior.

Having said that, there has been a boom in the number of people cycling to work in the last 10 years. There are two main reasons for this. One is the low availability/high cost of car parking in the city and surrounding suburbs. The other is that we get the Tour de France televised on free to air, during prime time for the entire tour. That has driven a huge increase in road cycling and even non-cyclists like to watch and talk about what is happening in the Tour.