It’s a pretty universally known fact:
That you can determine the age of a tree by the number of rings it has.
But with certain mammals, you can also apply the same logic to determine their age.
Mountain goats, for example:
Develop a seasonal ring on their horns. Their age is equal to the number of rings they have minus one. (Source: Reliability of Age Determination of Mountain Goats. Stevens, Victoria)
With the Scottish Feral Goats:
The number of rings on their horns will correlate precisely to their age.