Feeding an old billy goat
The barn where I board my horse has a resident old, white billy goat inherited from the farm next door. What is OK to feed the goat? People bring in molasses treats and otherwise he roams around the barn eating hay, grass, and weeds. He is old but I can feel his ribs and wonder if that is normal, or if he isn't getting enough to eat of the right foods.
Based on the information you are providing, the goat appears to be in thin condition. This may be due to lack of nutrition or age-related decline. You indicated that the goat is a billy and it is old. Older goats, like other animals, tend to wear out their teeth making feeding difficult for them. This can cause them to become thin. There are also some breed differences, and if this is a dairy breed, he would generally appear thinner than a meat breed. But if his ribs and back are visible, he most likely is in thin condition.
The items you listed are fine to feed goats. Be cautious of him getting something out of the trash or lying around that may cause blockage of his digestive system, as they will chew almost anything. Goats should be fed a good quality forage or hay and supplemented with grain when the diet is not adequate. A mature male goat should be able to obtain enough nutrition from good quality hay to maintain his body weight, if he is not in a breeding pasture with a large number of does.
If you are concerned about the condition of the goat, view the video on body condition scoring at: http://www.extension.org/pages/30651/body-condition-scoring. This will give you the information needed to determine if the nutrition he is receiving is enough. If he is a condition score below 2, he should be offered better nutrition. Check his teeth as well to make sure he has good sound teeth (goats will only have bottom front teeth) that will allow him to graze and eat properly. If his teeth are worn, he will not be able to chew the forage provided. For diet information, a couple of good references are on the eXtension website at: http://www.extension.org/pages/19333/goat-nutrition.