Some whales have gestation periods even longer than this. For example, the sperm whale and pilot whale have gestation periods of 15 or 16 months. Additionally, each group contains young males and sometimes one, occasionally two, adult males.
Adult males are much larger than adult females so large animals are most always males.
So whales are mammals and not fish. Because of that, the most important ways they differ from fish have to do with the fact that fish evolution all took place in the water, while much of the evolution of whales took place on land. This means that whales have a lot of traits and behaviors that land mammals have and that fish don't have. Whales are airbreathers with lungs while fish breathe with gills. If you replace the hind limbs of a land mammal with a whale tail, the arching backbone that once sent a cheetah across an African plain can also send a fin whale through the ocean.