Most slicing cucumbers mature when they reach about 8 inches long, and before they turn yellow. Pickling cucumbers are smaller and used for canning purposes. Lighter green in color, they have a warty surface and a blockier shape. They can also be eaten fresh, but get hard and bitter if they become too large. Do not plant a pickling type cucumber and try to use it as a slicer.
Cucumbers are monoecious plants, meaning they have both male and female flowers on the same plant.
The male flowers usually bloom first in early summer while the female flowers wait until warmer weather later in the summer. I suppose the male is sent first to check things out and make sure all is safe. Since the first few flowers are male, they do not produce fruit. I receive many calls every year from worried gardeners who see blossoms but have no fruit. Eventually the female flowers will emerge and set a small fruit next to the vine.