This linguistic confusion is why Americans call the Pennsylvania Dutch Dutch even though they're Germans. To review: this country is the Netherlands, its people are Dutch, they speak Dutch. There is no country called Holland, but there are provinces of North and South Holland.
In clean, uncrowded conditions in tanks or ponds, goldfish grow fast. They can grow to a few inches (1 to 4 inches) within the first year. It really depends on their genetics and living situation. It may take a year or two before they change color from brown to gold or whatever color their parents were.
A more common size would be about 12 inches for a common and about 8 to 10 inches for a fancy. They will grow faster, but not necessarily ultimately larger, in large ponds than in aquaria. People who say they get to be three feet long probably have goldfish confused with koi or other carp.