You can donate blood if you are generally in good health. You also need to be aged between 17 to 65 years and weigh at least 110.2 lbs (50 kg). When you know you are donating blood drink up in the 24 hours before donation, especially in warm weather and have at least 3 good-sized glasses of water in the 3 hours before donating.
Yes a normal and healthy person can donate blood, and should donate it. If your weight is around 45 kg, 15 yrs of age, no major ailments in last 3 months, no chronic diseases, HIV negative, no hepatitis, typhoid and sickle cells etc.