That depends on who you ask. The U.S. Food and Drug Administration (FDA) recommend 50 grams of protein per day for anyone over 4 years old. This number is based on a 2,000 calorie diet, and as you can imagine, is pretty generic.
Since protein acts as the building blocks of life, a more reasonable way to calculate your needs is based on your body mass. The U.S. Department of Agriculture (USDA) suggests a simple equation where you can multiply your body weight (in pounds) by 0.36 for your daily requirement.