In the United States, there are approximately 3,381,150 Registered Nurses. [1]

A survey of 516 female optometrists stated that about 23.3% preferred  wearing skirts/dresses to work.  This means that approximately  93,000 of our nursing group prefer wearing skirts to pants. [4]

Out of that number, roughly  9% of nurses are male, and 91% are female. This leaves us with about 3,076,846 female nurses [2]

Based on this information, I think that it is reasonable for my line to reach about 60% (55,800) of the 93,000 nurses. 

In the United states, approximately 13% of the population are females aged 20-40. This means that of our nurses there are about 399,990 in the target age range. [3]