Aging animals requires knowing what to look for. Although you may be able to venture a rough guess at a glance, you probably won't be able to accurately decipher an animal's age from this alone. White-tailed deer usually give birth in the late spring or early summer and the fawns stay with their mothers until they are yearlings. There are different methods you can use to determine a fawn's age.
Observe how many spots the fawn has. A fawn that still has a lot of spots on its back is fairly young, less than 4 months or so, whereas an older fawn will have lost these distinctive markings as its winter coat grows in.
Look at the fawn's teeth, if possible. The number of teeth, as well as the kinds of teeth, indicate its age. A fawn starts out with just a few teeth, called milk teeth, at the front of its jaw. At half a year old, the fawn will have more teeth but fewer than six. When the fawn is a year and a half old, it should have six teeth.
Measure the fawn's hoof size. Young fawns have hooves that measure about 3 inches long, while a yearling's hooves are closer to 4 inches or more. The easiest way to measure hoof size is to inspect the deer's tracks.
If you think you have found an abandoned fawn, leave it alone until you are sure. Sometimes, a mother deer will leave her baby alone for hours before returning.