Im a 20 years old male and im 60 kg , i've always been skinny and i have never had a good diet , and my father and brother are hairy but i don't?

Eat a balanced diet: If you are concerned about how you look, the first thing is to eat a balanced diet with enough calories for your age and level of activity. Being malnourished could prevent you from developing healthy body hair. See your doctor to run blood test.

Fitness: You are at your physical and intellectual prime. You owe it to yourself to find some sport in which you'll enjoy working your body hard. Get reacquainted with how good lean protein, fruits and vegetables are, and befriend and eat with serious athletes. I can't promise you'll grow more body hair but if you're getting normal erections / ejaculations your hormones are fine -- if not, tell your doctor