In Denmark anything less that 16.5% can be purchased by 16 year olds.

This is crazy. 16.5 is stronger than regular wine.

That's exactly the point. It's a middle ground ABV where there aren't a ton of products and below which are mostly fermented beverages and above which is distilled liquor.

I was talking about Germany.

Belgium as well.

In Switzerland, it is 16 for beer and wine, and 18 for spirits (or drinks that contain spirits, like "alcopops", even if they have a low ABV). I think Austria and Germany are the same.

Most US states, last I checked. Note: drinking age, not age to buy alcohol. Usually there's some rule about parental consent or only at home.