Hi, a chihuahua 14 to 18 months reaches full growth. But they may add more weight with extra feedings. Saw once a chihuahua at one year old that weighed 9 ozs. Had a chihuahua 4 yrs of age at one pound and 2 ounces.
A goat or sheep are considered adult at 12 months old. However, an uncastrated male is fertile at about 4 months and a female may breed before 12 months.