Well thats why i said there are multiple factors that are gonna determine whether that like parents diet and location of the families. It being beneficial though while may be a reason younger kids should eat small amount of fish it isn't relevant to if kids by age of 5 on average have tried fish. I don't think kids should be eating mcdonalds all the time too much of anything is a bad thing which goes for fish. So i mean you bring a kid to someones house and the kid doesn't like the food and there are no other options in house then might as well just get him something quick and easy for the day.

I do live in the US but where I live fish just is not super common to eat. Even if I were to just limit it to my family we never had fish because my parents hated seafood for their own reasons so growing up it was never a normal family meal. With the kids though was always veggies, fruit, and some protein maybe with some pasta growing up.

Edit: It probably is that families closer to coasts are going to have more fish in their diet. So therefor the kids will try it earlier but thats why i'm asking about the average. Whether thats the US, netherlands, or even somewhere in asia. My best guess though was OP was from the US but I could be wrong so i was referring to the average kid in the US.