Can a diabetic old person can drink whey protein to get some strength?

You need to read some books about nutrition and learn how to eat right. Protein shakes are made of powdered milk, soy flour, sugar, and flavor. They cost about $1.25 for the amount of protein you get in a quarter's worth of milk. Your body needs 4/10 gram of complete protein per pound of weight, about 65 grams for a female and 90 grams for a male. You do not need more because you exercise or less because you loaf. For convenience you only count 6 grams per egg, 12 grams per glass of milk, and 24 grams per quarter pound of meat. If you eat more than the body needs, the excess is burned as ordinary but expensive calories. If you really think you need more protein, get powdered milk and mix it into your food. Or just eat more eggs.