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.
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