You need protein for your muscles, bones, and the rest of your body. Exactly how much you need changes with age: 1  Babies need about 10 grams a day. 2  School-age kids need 19-34 grams a day.3  Teenage boys need up to 52 grams a day. 4  Teenage girls need 46 grams a day. 5  Adult men need about 56 grams a day.6  Adult women need about 46 grams a day (71 grams, if pregnant or breastfeeding).xactly how much you need changes with age: 1  Babies need about 10 grams a day. 2  School-age kids need 19-34 grams a day. 3  Teenage boys need up to 52 grams a day.