I'm quite thin for my height 160 lb for a 6 ft 4 in male. will milk benefit me to grow in size in a healthy way?

Ur BMI is 20 normal: Have you seen a doctor? Get lab, history, exam. Is not your weight , is how physically fit you are. If you feel sick, weak, loosing weight, diarrhea etc then i'll be concerned. Bmi of 20 is normal range. Again, is how you feel. Make sure you have excercise routine that incorporate (cardio, strenght, flexibility), eat healthy, have a positve mental attitude (pma). In time you'll gain weight (age).