To determine the age of a peacock, you will need to look at a few different physical characteristics. The first is the size of the bird. An adult peacock will be much larger than a juvenile. The second is the color of the plumage. A young peacock will have brown and green feathers, while an older peacock will be mostly blue and green. The third is the number of tail feathers. A peacock will grow a new tail feather each year, so the number of feathers can be used to estimate the age of the bird. Finally, you can look at the condition of the beak and claws. A peacock that is getting old will have a duller beak and claws that are not as sharp as they once were.