There are a few ways of guessing how old a chicken is.... * Size.

Obviously, if the chicken is still small, it is probably under a year of age, depending on the breed. * Feathers.

The presence of feathers is a good way to tell age in young chickens. The presence of down, and little to no feathers indicates the chick is very young. Then there are "adolescent" feathers, and then full grown adult feathers. * Breast Bone.

If you are guessing the age of a hen, gently flip her over on her back, and feel of her breastbone. If it is very hard and rigid, she is over one year. If it is more soft/flexible, she is under a year. * Tail Feathers.

Especially with roosters, the tail is a nice way of guesstimating age. If the tail is full and nice, the cock is older. Also, the presence of fully formed saddle and hackle feathers is a good way to guess if a rooster is fully matured. * Spurs

Up to a certain age, the size of the spur can be a nice identification for roosters as well. A smaller spur means a younger rooster, while longer/more pronounced spurs mean the cock is older.