In the Netherlands you're either a tourist or 60 year or older if you wear a helmet. But it is also not that fair to compare the Netherlands to other countries. We grew up with bicycles and our infrastructure is much better for cycling.
I suspect people don't like comparing with the Netherlands because it doesn't support their biases in this argument
It's more that the Netherlands is a substantial outlier in terms of how they accommodate cyclists, so applying their attitudes towards helmets without also being as cyclist-friendly (infrastructurally and socially) as they are is asking for trouble.
Obviously infrastructure helps a lot, but there is still the danger inherent in the fact that it's quite far from your head to the ground. I don't wear a helmet though personally, since the bike infrastructure is good in my city in Germany, at least on the routes I take