Goats, like all animals, go through various life stages. At birth, goats of both sexes are called kids, and like human kids, they are curious, high-spirited and full of energy -- caring more for play than almost anything else except, perhaps, momma's milk. A yearling goat has passed beyond that first kid stage to that of a young adult going into his second year. Yearlings are almost mature goats, and will show more interest in herd mates and less dependence upon their mothers as they further develop.
Not Just a Yearling
Both male and female goats get lumped together under the name “kid” until they approach sexual maturity, when they are generally reclassified as either does, wethers or bucks. Yearling or younger females who have not yet produced offspring are often called doelings. Since male kids sexually mature even earlier than females, those who are not wanted for future stud service are routinely neutered very early and remain sexually inactive their entire lives. Those young males are then called wethers. Young intact males are sometimes known as bucklings before they become fully mature bucks.
The First Year
Although by the end of a kid's first year she is sexually mature and nearly full-grown, she will continue to add weight and develop physically and emotionally for at least another year or two. During her first year, a kid will replace her middle two baby teeth with larger, adult incisors, and continue -- over the course of four years -- to lose all her baby teeth and gain permanent replacements.
The average goat is capable of reproduction at a surprisingly early age -- females of some breeds will reach puberty as early as 4 months old, and male kids are capable of fathering offspring at the ripe old age of only 2 or 3 months. Toward the end of the first year, does will enter their first estrus and are sometimes bred, though many goat breeders agree that it is better to wait until does reach 60 percent of their mature weight and are in good health before breeding.
It is usually OK to keep all kids together during the first couple of months, but it is good practice to separate intact bucklings from the rest of the herd at that point to prevent unwanted pregnancies. Wethers often remain with the herd or are sold as pets or as meat within their first year.
From Yearling to Maturity
A mature goat is full-sized and both physically and emotionally developed by the third year. Though all female goats of every age are technically does, and yearling does are often called doelings, the name "dam" is only employed to describe a female goat who has successfully produced kids. Many old-time goat breeders may also call fully mature females "nannies" -- whether they have produced offspring or not. Mature male goats are bucks, but the nickname "Billy" is frequently used as well. Maturity covers the years from around 3 to upwards of 16 years. Non-breeding pet goats of both sexes, especially wethers -- with no sexual stress to prematurely age them -- usually live longest of all.
Yearlings for Pets
If you only want pet goats, consider buying or rescuing unwanted yearlings rather than younger kids. With yearlings you can more readily see what you will get as an adult, while simultaneously avoiding the hassle of bottle-raising babies. Yearling wethers are a wonderful choice as they retain many of the playful, affectionate characteristics of sexually immature kids, remain docile and sweet and never develop the strong odors and often rather disgusting habits of the mature buck. A mixed pair of yearlings -- wether and doeling -- is another good choice for pets. Goats form strong friendship bonds with one another, and should never be kept alone. A mother and kids, or a pair of twins of either sex -- so long as males are not intact -- are nearly always good choices, as their bonds will have formed from birth.