My Nigi/pygmy doe who turns 8 years in 5 days started " joint crunching/popping" when she turned 6 years...I simply attributed it to the extra weight she had been carrying with each pregnancy, she's healthy otherwise. As far as age goes, if she is horned SOMETIMES you can tell by the size and length of the horns, most times you go by the bottom front teeth...there would be 8 teeth in the front bottom of the mouth if they are long, stained or worn looking the goat is over 4 years old, if you see that the middle six look different than the outer 2 then the goat is around 3 years...if there are not 8 teeth and they look worn and longish..the goat is older than 8 years. Really good if you have a goat and know exactly how old it is to do a comparison...baby teeth erupt from birth to a year of age then with each birthday up to 4 years old they get their permanent teeth.( this includes the molars...top and bottom)
I know that sometimes it's really hard to pass up "auction barn rescues" but most of the time the goats that are passed thru there are the goats that didn't do well with kidding or are culled from their herd for other reasons, this is entirely up to you if you want to bring a possibly diseased goat to your property and possibly infect the area and make it bad for healthy goats, sometimes sale barns are great and other times it's best to purchase from a reputable breeder.