Unfortunately, there is presently no package dating that would allow you to assess the age of the food. Guinea pigs uncommonly form tumors. Bloody urine is a serious sign and may indicate infection or stones of the bladder. Guinea pigs are often found to be losing hair, sometimes with itching and dandruff. This can be a result of many things including mange, ringworm, fur mites and Vitamin C deficiency.
Ringworm is potentially contagious to people.
Poor cage sanitation can lead to disease.