To build muscle strength and limit age-related muscle loss (sarcopenia), older men should consume extra protein after doing strength-building exercise, concludes an analysis of 17 clinical trials involving people over 60 (average age 73 overall), published in the American Journal of Clinical Nutrition.
Most studies lasted 12 to 24 weeks; the amount of extra protein ranged from 10 to 35 grams, usually in the form of whey or milk protein or milk-based beverages, and the strength-training regimens varied. While extra protein had a significant effect on exercise-induced muscle gain in men, this was not seen in women. Not surprisingly, greater muscle gains were seen in longer studies that involved training multiple body parts.
Milk has 8 grams of protein per cup, yogurt 10 to 20 grams per cup (Greek yogurt has the most). It isn't hard to get enough protein from food.
Since high protein consumption can worsen chronic kidney disease, check with your doctor before upping your intake.
Also see Do You Need More Protein?