My brother is over six feet tall. We are of Dutch descent and the Dutch are frequently very tall. 
Oh I didnt know that Dutch people tend to be tall interesing
Yes, Dutch people are tall, though height can serve as indicator of health and good nutrition. 
on average how much taller are they then US males do you know
It depends, height increases with a populations' genetic profile. 
interesting, is there a specific reason, I guess just genetics
Studies show that there is a correlation between small stature and a longer life expectancy. Individuals of small stature are also more likely to have lower blood pressure and are less likely to acquire cancer. The University of Hawaii has found that the “longevity gene” FOXO3 that reduces the effects of aging is more commonly found in individuals of a small body size. Short stature decreases the risk of venous insufficiency.
When populations share genetic background and environmental factors, average height is frequently characteristic within the group. Exceptional height variation
to increase their number and diversify the gene pool, while preserving the health of the breed.
Description.
Description Appearance.
The Dutch Shepherd on average weigh between and the height varies between 55–63 cm (approximately 22 to 25 inches tall at the withers). Depending on the coat, the breed can be distinguished as short-haired, long-haired, or rough-haired.
Short-haired: All over the body, quite hard, close-fitting, with woolly undercoat. Ruff, breeches